Simulation and Optimization of a Hydrogen Internal Combustion Engine

Simulation and Optimization of a Hydrogen Internal Combustion Engine July 2016 Leonor Ferreira Bessa Babo Dissertação do MIEM Orientador no BIT: Prof. Bai-gang Sun Orientador na FEUP: Prof. Carlos Pinho Faculdade de Engenharia da Universidade do Porto Mestrado Integrado em Engenharia Mecânica Simulation and Optimization of a Hydrogen Internal Combustion Engine ii [Blank Page] Simulation and Optimization of a Hydrogen Internal Combustion Engine iii “一步一个脚印儿” by Laoshe （老舍） “Every step leaves its print” by Laoshe Simulation and Optimization of a Hydrogen Internal Combustion Engine iv [Blank Page] Simulation and Optimization of a Hydrogen Internal Combustion Engine v Abstract This work was developed within the framework of discipline Dissertation, of the 5th year, of Thermal Energy branch of the Master Degree in Mechanical Engineering of Faculty of Engineering of the University of Porto (FEUP) and was carried under a partnership agreement with the Vehicle Engineering Laboratory of the Beijing Institute of Technology. In this document it is presented an overall review of hydrogen fueled internal combustion engines. Subsequently, using WAVE software, an analysis of break power output of a hydrogen engine changing the intake parameters is made. Using the same software, an optimization of the intake and exhaust valve timings of opening and closing was made. Finally, a general analysis on the influence of ignition timing, air fuel equivalence ratio and throttle angle on the respective torque response of the engine was carried out. Key words: hydrogen internal combustion engines; WAVE software; Simulation and Optimization of a Hydrogen Internal Combustion Engine vi [Blank Page] Simulation and Optimization of a Hydrogen Internal Combustion Engine vii Resumo Este trabalho foi desenvolvido no âmbito da disciplina Dissertação, do 5º ano, da opção Energia Térmica do Mestrado Integrado em Engenharia Mecânica da Faculdade de Engenharia da Universidade do Porto (FEUP) e em parceria com o Laboratório de Engenharia Automóvel do Beijing Institute of Technology (BIT). Neste documento é apresentado o estado da arte dos motores de combustão interna com combustível de hidrogénio. De seguida, recorrendo ao programa WAVE, é feita uma avaliação da potência efetiva do motor a hidrogénio alterando as condições de entrada do combustível. Ainda com o mesmo programa foram otimizados os tempos de abertura e fecho das válvulas de entrada e saída do motor. Por fim, foi feita uma análise geral de influência do tempo ignição, razão ar combustível e ângulos de abertura e fecho da válvula de admissão, sobre o binário efetivo do motor. Palavras-chave: motores de combustão a hidrogénio; programa WAVE; Simulation and Optimization of a Hydrogen Internal Combustion Engine viii [Blank Page] Simulation and Optimization of a Hydrogen Internal Combustion Engine ix Acknowledgements Long was the way to get here. My express gratitude goes to Beijing Institute of Technology and University of Porto for offering me the opportunity of doing this project in Beijing, China. To professor Baigang Sun for receiving me so well in vehicle laboratory of BIT. To PhD Student and co-supervisor Xiao-Luo for all the support even on weekends. To all my colleagues in the laboratory. I would specially like to thank, Professor Carlos Pinho, that accepted being the professor supervisor of this project and whose help was essential. Finally, to my family for all the support during my stay in China. Simulation and Optimization of a Hydrogen Internal Combustion Engine xvi Symbol Description Units  Air-to-fuel equivalence ratio a Combustion efficiency  Crank angle  Fuel-to-air equivalence ratio γ Specific heat ratio [J/K]  0 Start of combustion crank angle ∆R Uncertainty on the computed result 1 1. Introduction This project will be divided in three main stages. Firstly, the motivations for the need of alternative energies to the fossil fuels, and a deeper analysis of the energy consumption and CO2 emissions in China will be carried out. Then, it will be made a literature review of the hydrogen as a fuel: state of art, developments and technologies. An economic and environmental analysis of the various options will also be taken into account The second part of the project, will be through the use of the software Ricardo WAVE, the simulation of different combustion conditions of hydrogen in a virtual engine, followed by an analysis of the results. The last step, will be a practical approach using a laboratory to do some tests and compare the experimental with the numerical results. 1.1. Motivations Combating pollution and emissions is a must to reduce the global warming. With the COP21 (climate change agreement) treaty signed in December 2015 by China and 195 other countries, there is now a global compromise to reduce of greenhouse emissions and to set a goal of limiting global warming to less than 2 degrees Celsius (°C) compared to pre-industrial levels. China, being the most populated country in the world and with prospective of growing 45 million people in the next 5 years, needs to search for new and renewable energies [1]. It is also the country in the world with highest energy consumption and CO2 emissions. This is caused not just because of the large population but also due to the highly industrialized areas and the fossil fuel used in transports. Nowadays, there are many areas of research to create sustainable energy systems. The use of hydrogen as an energy carrier is one of the options put forward [2]. Simulation and Optimization of a Hydrogen Internal Combustion Engine 2 [Blank Page] Simulation and Optimization of a Hydrogen Internal Combustion Engine 3 2. Literature Review 2.1. The need for clean energy in transports The search for new fuel alternatives is motivated by the trends in petroleum prices and environmental problems caused by the use of these. The introduction of alternative fuels has to combine technical feasibility, environmental impact and economic viability. Transport accounts for 25% of global CO2 emissions and is one of the few industrial sectors where emissions are still growing. The current trends point to a growth of 50% by 2030 and 80% by 2050, which makes it unsustainable. Worldwide, population and incomes rising is strongly related with transport sector energy and CO2 trends while the transport sector continues to rely primarily on oil [2]. Figure 1 - CO2 emissions from transport [2] Looking at the evolution of the CO2 emissions from 1990 until 2013, it increased by 68% in road sector and accounted for three quarters of transport emissions in 2013. For the international transport, the growth of people travelling and the growth on importation and exportation of goods made the marine and aviation to grow even faster, 64% and 90% in 2013 than in 1990 respectively [2]. Current and emerging technologies which have the potential to reduce substantial CO2 emissions should be rapidly introduced. Simulation and Optimization of a Hydrogen Internal Combustion Engine 4 2.1.1. China Concerning data from 2013 and considering all sectors of CO2 emissions, China was responsible for 29% (10.3 billion tons) of world CO2 emissions followed by U.S. responsible for 15% of the emissions (5.3 billion tons) and the European Union with 11% (EU28) (3.7 billion tons) [2]. China is, at the moment, the largest industrialized nation and in result of this there is a growing demand for energy. The increasing imports of energy, particularly petroleum, has got global attention, specially regarding the corresponding greenhouse gas emissions. Since the end of the 1970s Chinese vehicle industry developed massively. During the last three decades, the road vehicle population increased from 1.36 million units to 70 million units [2]. Its per capita reserves of coal, petroleum and natural gas (NG) are 67.0%, 5.4%, and 7.5% of world average reserves, respectively. However, these reserves cannot fulfil all the country demand for petroleum by the increasing of vehicles, which makes China become a net petroleum importing country since 1993. In response to population growth and rise of income there is a continuous increase in private vehicle ownership. Figure 2 illustrates a projection of vehicle ownership in China up to 2050, considering three different scenarios [3]. Figure 2 - Projected Chinese vehicle ownership [3]. The boom in China’s automotive industry poses a great challenge to the environment, especially in relation to greenhouse gas (GHG) emissions. It is therefore essential to promote the use of low-emission vehicles. New strategies should be considered to increase vehicle energy efficiency standards, changing consumer energy consumption patterns and reducing the transportation sector high dependency on fossil fuels [3]. Simulation and Optimization of a Hydrogen Internal Combustion Engine 5 2.1.2. EU-28 and Portugal Data from 2012 of the energy consumption distribution in EU-28 by sector shows that residential, road transport and industry accounted for the biggest shares, 26 % each. The service sector accounted for 13 %, transport for 6 % and the other remaining sectors for 3 %. As far as the energy dependency in 2012 was concerned, the highest need was for petroleum products, 24 million TJ, of which 93 % were imported [4]. The transport sector is responsible for the second greenhouse gas emissions in the EU. More than two thirds of transport-related greenhouse gas emissions are from road transport. Greenhouse gas emissions in other sectors decreased 15% between 1990 and 2007, but emissions from transport increased 36% during the same period. This increase has happened despite improved vehicle efficiency because the amount of personal and freight transport has increased. There was also an increase in number of cars per inhabitant between 2006 and 2012. Since 2008, greenhouse gas emissions from transport have started to decrease. Despite this trend, transport emissions were in 2012 still 20.5 % above 1990 levels [5]. In Portugal, the transport sector is the biggest energy consumer, accounting with 36%, followed by the industry sector, 31%, and the residential sector, 17%. The transport sector is responsible for 24% of greenhouse gas emissions. Portugal is still, as most of EU-28, very dependent on fossil fuels. In figure 3 are represented the greenhouse gas emissions for the transport sector from 1990 until 2013 for EU-28 and Portugal (ratio of 2000 = 100 emissions) [6]. Figure 3 - GHG emissions in transports, UE-28 and Portugal [6] Considering the GHG emissions originated by Portugal, they were almost always below EU-28 average, except during the years between 2000 and 2004 [6]. Simulation and Optimization of a Hydrogen Internal Combustion Engine 6 2.2. Attractiveness and drawbacks of hydrogen as a fuel for internal combustion engines There are plenty of options on how to produce hydrogen, which have been studied until now, some more developed than others. What attracts the most is the long-term viability of some of them, such as renewable energy (biomass, wind, solar) and virtually zero harmful emissions, although at the moment most of the production is made from fossil fuels [7]. Using hydrogen as an energy carrier has still many challenges to overcome. It is difficult to keep a good compromise of cost and efficiency, considering all distribution, bulk storage and onboard vehicle storage. Bearing in mind all aspects of hydrogen-fueled vehicles compared to hydrocarbon fuel, care must be taken to ensure that the well-to-wheel greenhouse gas emissions are reduced. Another aspect is the possibility of using an ordinary ICE that is suitably adapted and compatible to work either with hydrogen or other fuels and still keeps a good performance. However, the H2ICEs still need much development, thus it is still not possible to combine high efficiency, low emissions, adequate specific power output and durability all in one concept. Moreover, several attempts to optimize engine fuel injection strategies always had the same result: high injection pressures. This limits on-board hydrogen storage options either: liquid hydrogen is stored in cryogenic tanks, and injection pressures are generated onboard, or compressed hydrogen is stored but then the full tank capacity cannot be utilized [8; 9; 10]. 2.3. Combustion properties of hydrogen Previously, the attractiveness and drawbacks of hydrogen were shown, now its physical and chemical properties are presented. Table 1 presents a comparison of different properties for hydrogen and more conventional fuels. The hydrogen molecule is very small, light and mobile and at atmospheric conditions has a very low density. Its wide range of flammability with an air-to-fuel equivalence ratio  extending from as lean as  = 10 to as rich as  = 0.14 allows a wide range of engine power output through changes in the mixture equivalence ratio. The low lean-flammability limit of hydrogen increases with pressure and allows stable combustion at highly dilute conditions, while the upper flammability limit has a fairly complex behavior in terms of pressure dependence but lesser importance to engines. Hydrogen has a small quenching distance of 0.64 mm compared to 2.0 mm for gasoline, under stoichiometric conditions. This is the distance from the cylinder wall where flame front extinguishes. It is minimal for mixtures around stoichiometry, and decreases with increasing pressure and temperature. This means it is more difficult to extinguish the hydrogen flame and implies more susceptibility of the engine to backfire since the hydrogen-air mixture flame more easily passes through valves and very small gaps than the gasoline-air mixture flame [11; 12]. Simulation and Optimization of a Hydrogen Internal Combustion Engine 7 Hydrogen has high flame speed of combustion. For stoichiometric mixtures, the flame speed slows down, improving the fuel economy and reducing the nitrogen oxides, but it is still a much higher flame speed when compared to gasoline-air mixtures. Flame speed and maximum combustion temperature are of prime concern for thermal efficiency and emissions [11]. The low boiling temperature of -253 °C makes liquid hydrogen storage at atmosphere pressure very challenging. The extremely wide ignition limits of hydrogen compared to any other fuel makes it extremely well suited for lean operation with its positive effect on engine efficiency. Although it can be the main cause for abnormal combustion, see section 2.8.1. The minimum ignition energy of hydrogen at stoichiometric conditions is approximately 0.02 mJ while for gasoline, Diesel or methane it is in order of 0.25 mJ. Only at an air/fuel ratio as lean as   4 does the required ignition energy of hydrogen reach the value of conventional fuels at stoichiometric conditions [13]. The theoretical thermodynamic efficiency of an Otto cycle engine, used on H2ICE’s, is based on the compression ratio of the engine as shown in equation (2.1)  𝑡ℎ =1−(1 𝑟𝑐)𝛾−1 (2.1) From the above equation the higher the compression ratio rc or the specific heat ratio γ, the higher thermodynamic efficiency of the engine. Hydrogen has a much simpler molecular structure than gasoline and therefore its specific-heat ratio is higher than that of gasoline. In this sense, theoretically, hydrogen engine can have higher thermal efficiency compared to gasoline engine [8; 11]. Table 1 - Properties of Hydrogen Compared to Fossil Fuels [8; 14; 15] Parameter Diesel Gasoline Methane H2 Density [kg/m3] 830 I 730-780 I 0.72 I 0.089 I 71 II,III Stoichiometric air demand Lst [kgair/kgfuel] 14.5 14.7 17.2 34.3 Lower heating value [MJ/kg] 42.5 43.5 50 120 Boiling temperature III [C] 180-360 25-215 -162 -253 Ignition limits IV [] 0.5-1.3 0.4-1.4 0.7-2.1 0.14-10 Minimum ignition energy III, IV, V [mJ] 0.24 0.24 0.29 0.02 Self-ignition temperature [C] ~250 ~250 595 585 Specific heat ratio III, VII [γ] 1.389 1.354 1.401 Laminar flame speed IV, V [cm/s] 40-80 40-80 40 200 Quenching distance III, IV, VI [mm] 2 2.03 0.64 Carbon content [Mass-%] 86 86 75 0 I at 1.013 bar, 0C II at -253C III at 1.013 bar IV in air V =1 VI at 20C VII at 300 K Simulation and Optimization of a Hydrogen Internal Combustion Engine 8 2.4. Production Though hydrogen is the most abundant element in the universe, there is no natural hydrogen gas resource on Earth effectively. It is combined with other elements, which means that it can be produced from a variety of feedstocks containing hydrogen compounds. Hydrogen gas is not a primary fuel in the same sense as natural gas, oil, and coal. Rather, hydrogen is an energy carrier, like electricity. It is a secondary form of energy, produced using other primary energy sources, such as natural gas, coal, as well as renewable resources. Figure 4 shows some of the feedstocks and processes to produce hydrogen. There is a variety of process technologies that can be used, each of them is in a different stage of development, and offers unique opportunities, benefits and challenges. Factors such as the local availability of feedstock, the maturity of the technology, market applications and demand, policy issues, and costs will all influence the choice for hydrogen production [16; 17]. Figure 4 - Some feedstock and process alternatives [9] Although there are many production alternatives most of them are still under development. Currently, the most developed and most used technology is the reforming of hydrocarbon fuels, representing 96% of the production by fossil sources. Figure 4 shows the actual distribution of the most used feedstocks [18]. Simulation and Optimization of a Hydrogen Internal Combustion Engine 9 Each year, 8 EJ (about 190 Mtoe) of hydrogen are produced, 40% are used in chemical processes (manufacturing of ammonia and synthesis for methanol), 40% in refineries and 20% in food, electronics and metallurgical processing industries. Only a fraction of this hydrogen is currently used for energy purposes. Most of this hydrogen is produced on-site in refineries and chemical plants for non-energy uses. The global market for hydrogen is already greater than US$40 billion per year [19]. In 2007, the hydrogen production amount in China was about 12.42 million tons per year being the production distributed by coal, natural gas and oil in the percentage of 57.3%, 23.0% and 19.7% respectively [20]. 2.4.1. Hydrogen produced from conventional sources As seen before the major production of hydrogen, nowadays, come from conventional sources of fossil fuels. In this section are presented the different methods of obtaining hydrogen. 2.4.1.1. Steam reforming of natural gas There are three primary techniques used to produce hydrogen from hydrocarbon fuels: steam reforming, partial oxidation (POX), and autothermal reforming (ATR). The reforming process has the most industrial experience, although it is the one with highest pollutant air emissions. It consists of producing a gas stream composed primarily of hydrogen, carbon monoxide and carbon dioxide. Endothermic steam reforming of hydrocarbons requires an external heat source, compared to POX and ATR has a lower operating temperature. Steam reforming does not require oxygen and produces reformate with a high H2/CO ratio (3:1). Partial oxidation converts hydrocarbons to hydrogen providing heat by a controlled combustion. The process occurs at high temperatures with the formation of a low H2/CO ratio (1:1 to 2:1). POX has been proposed for use in hydrogen production for automobile fuel cells and some commercial Natural Gas 48% Coal 18% Oil 30% Electrolysis 4% Figure 5 - Feedstock used in the current global production of hydrogen [18]. Simulation and Optimization of a Hydrogen Internal Combustion Engine 16 used for tanks can be carbon fiber-resin composite-wrapped with high density polyethylene (HDPE) or aluminum liner. The graphic of figure 11 shows an example of the weight and volume distribution of a 350 bar tank system capable of carrying 5.6 kg H2 [17; 25; 26]. Figure 11 - Weight and volume distribution for compressed hydrogen storage systems [27] For the weight distribution carbon fiber accounts for 53%, followed by the weight of other components such as valves, pressure regulators, tubes, etc. that account with 19%. Other contributors to the system weight are the liner (11%), glass fiber (6%) and foam (5%). For the volume distribution the largest contributor is the hydrogen (81%), with less than 5% each of the liner, foam, glass fiber and the other components [27]. 2.5.2. Cryogenic liquid hydrogen The most common way to store hydrogen in a liquid form (LH2), and at ambient pressure, is to cool it down to cryogenic temperatures (–253 °C). Liquid hydrogen is stored generally in insulated, passive storage systems, meaning that no active cooling is provided. Despite this, the remaining heat input causes liquid hydrogen to evaporate (about 2-5% of the volume evaporates), which increases the pressure. Thus it requires a system with continuous consumption or at least free release to avoid pressure increase. The main advantage with liquid hydrogen is the high storage density that can be reached at relatively low pressures. The LH2 for internal combustion engines does not have to be injected as a liquid. For practical application a LH2 internal combustion engine fueling system typically requires a vacuum-jacketed fuel line, heat exchanger and cryogenic pumps, and injectors. Further developments are needed to be done in order to increase the capacity, to develop systems that automatically capture the boil-off and re-liquefy the fuel at competitive prices [17; 25]. H2 6% Other components 19% Foam 5% Glass Fiber 6% Carbon Fiber 53% Liner 11% Weight Distribution (%) H2 81% Other components 2% Foam 2% Glass Fiber 1% Carbon Fiber 10% Liner 4% Volume Distribution (%) Simulation and Optimization of a Hydrogen Internal Combustion Engine 17 2.5.3. Metal hydride storage Metal hydrides are the solid phase solution of hydrogen storage. They got most attention because of their capability of storing large quantities of hydrogen with higher volumetric densities than other storage options. The gravimetric hydrogen density of most metal hydrides is less than 3.0 wt.%. The main disadvantage, as represented in figure 10 by the red dot, is in the weight of the storage of alloys. The process consists in injecting hydrogen in gas form in a tank containing metal powder forming metal hydride. This way a solid phase solution is obtained and hydrogen is stored. To reuse the hydrogen stored the metal hydride goes through a thermal decomposition normally proceeded in a stepwise manner. Each step possesses its own thermodynamic and kinetic parameters. Desorption process occurs at equilibrium hydrogen pressures Peq and at temperature T, both parameters vary with hydride compositions. Most complex hydride systems encounter severe kinetic problems in desorbing hydrogen. Still, research needs to be done in order to increase absorption rate and operation temperature is still problematic [28; 29]. 2.6. Delivery Delivery is an essential part of all the hydrogen fueled vehicles facilities. It is very important to guarantee the transport hydrogen from a central or semi-central production facility to the final point of use. Also, hydrogen delivery infrastructure should provide the same level of safety, convenience, and functionality as existing liquid and gaseous fossil fuel based infrastructures. As seen before, hydrogen has many ways of being produced so that the delivery infrastructure will need to integrate these various hydrogen production options [30]. Figure 12 shows a description of the two methods of transporting gaseous H2. Transmission by pipeline requires a geological storage used to provide seasonal and surge capacity to the H2 and it is used for longer distance refueling station. High-pressure cylinders and tube trailers at 182 bar are commonly used to distribute gaseous hydrogen within 320 km of the source. Simulation and Optimization of a Hydrogen Internal Combustion Engine 18 Figure 12 - Gaseous delivery pathway: a) Pipeline transport b) Tube trailer transport [31] Based on extensive delivery system analyses, gaseous hydrogen transmission and distribution by pipeline is currently the lowest-cost delivery option for large volumes of hydrogen [31]. For the liquid hydrogen the delivery pathway is very different from the gaseous pathway, figure 13. First, the hydrogen changes phase from gaseous to liquid in a liquefier station. The energy cost for converting gaseous hydrogen to liquid is high; an estimate for current liquefaction is that the energy required about 35% of the energy content of the hydrogen. Then it is stored in a cryogenic tank at (-253oC) at the liquid terminal. A tube trailer that can carry up to 4000 kg of liquid hydrogen, with a leak of 0.5% transports the hydrogen to the fueling station. Hydrogen boil-off of up to 5% also occurs when unloading the liquid hydrogen on delivery [30; 31]. Simulation and Optimization of a Hydrogen Internal Combustion Engine 19 Figure 13 - Liquid delivery pathway [31] Another option of delivery that might reduce the cost and increase the volumetric efficiency of hydrogen storage is the use of solid carriers within the storage tank. This is identical to some of the approaches being researched for onboard vehicle hydrogen storage, figure 14 [30]. Figure 14 - Metal hydride delivery pathway [30] Stationary off-board storage does not have the same weight and volume restrictions of onboard vehicle storage, and systems that do not meet the goals for onboard storage might be effective for stationary off-board storage vessels. Each method of transport has many steps and many components involved. Alternative pathways could combine elements from two or three different approaches. As an example, gaseous hydrogen could be transported by pipeline to a terminal where it is liquefied for distribution by cryogenic tank trunk. To minimize costs, the logistics should be optimized, however it is only possible with the growing of the market. A fully developed system of delivery and infrastructures will take time to be built [30; 31]. Simulation and Optimization of a Hydrogen Internal Combustion Engine 20 2.7. Mixture formation concepts 2.7.1. External mixture – Port Fuel Injection There are only a few injectors specially developed for PFI hydrogen internal combustion engine, normally, natural gas injectors are the alternative. They require minimal change from a conventional engine structure, but results in limited power output. They can guarantee a uniform distribution of hydrogen between the cylinders providing a controlled combustion. Hydrogen injection systems for external mixture formation are operated at lower injection pressures (2–8 bar). Due to the relatively long time available for mixing of fuel and air, all external mixture formation concepts can be considered homogeneous and a dominating correlation between NOx emissions and air/fuel ratio can be established, figure 15 [12; 32]. Figure 15 - NOx emissions and air/fuel ratio correlation for PFI [9]. For fuel to air ratios ranging from 0.2 to 0.5 a hydrogen engine can operate without emitting NOx emissions. The excess of air available in the combustion chamber does not allow temperature rising to achieve the NOx critical value (~1800 K). The ability for the H2ICE to operate unthrottled is owed to the low lean-flammability limit and high flame-velocity of hydrogen. In this sense, hydrogen is an ideal fuel to apply a lean mixture without using a throttle for part load control. Not using a throttle valve has the advantage of eliminating pumping losses due to the pressure drop of the flow cross the throttle plate, and fuel efficiency is improved. [9; 33]. Beyond  =0.5 there is an exponential increase in NOx emissions due exceeding the NOx critical equivalence ratio, and the peak is reached for  ~0.75 (  ~ 1.3). The continuous increasing the engine load leads to a decrease in NOx emissions and being at stoichiometric conditions, it reaches around 1/3 of the peak value. This is caused because the combustion temperatures and the excess of oxygen decrease. External mixture formation is a better developed technology, therefore it presents higher engine efficiencies, extended lean operation range, lower cyclic variation and lower NOx production compared to Simulation and Optimization of a Hydrogen Internal Combustion Engine 21 direct injection. However, for high operating loads, delaying the injection timing for DI can result in significantly lower NOx emissions [34]. The theoretical power output for H2PFI is 86% of the corresponding gasoline output power. This difference is mainly caused by the low density of hydrogen, resulting in a significant decrease in mixture density when external mixture formation is being employed. An effective way to limit the power loss is by running hydrogen port-injection engines at stoichiometric air/fuel ratios [8; 12]. Simulation and Optimization of a Hydrogen Internal Combustion Engine 22 2.7.2. Internal mixture - Direct Injection Injecting hydrogen directly in the combustion chamber requires timing and duration strategy. These are crucial parameters influencing the NOx emissions. Adjusting the injection strategy can result in mixtures starting from fairly homogeneous (similar to external mixture formation) to strongly stratified. An early injection, shortly after intake valve closing, results in more homogeneous mixtures compared to late injection shortly before spark timing. As seen before for PFI, the overall air/fuel ratio strongly influences the NOx emissions. Figure 16 shows in a logarithm scale, the correlation between time of injection and air/fuel ratio with NOx emissions [13]. Figure 16 - Influence of injection timing and engine load (Air/Fuel Ratio) on NOx emissions in DI operation [15] Lean mixtures with  varying from 0.25 to 0.47 (in the legend  is represented by F) follow the same pattern, presenting higher emissions for late injection times. On the other hand, for rich mixtures the reverse happens. Late injection is expected to result in stratification, with zones that are even richer than stoichiometric, along with lean zones. This stratification avoids the NOx critical air/fuel ratio regime of  〜0.75 and thus reduces overall NOx emissions. DI has the advantage of working with higher loads without occurring abnormal combustion (backfire in particular). However, improvements need to be done to increase durability and maximum flow rate [15]. The optimal use of the DI-H2ICE can be achieved using a high-pressure (greater than 80 bar), high flow-rate hydrogen injector for operation at high engine speeds and overcoming the in-cylinder pressure for late injection in the compression stroke [35]. The theoretical power output for H2 DI exceeds in 19% the theoretical power output for the same engine operated on gasoline. Direct injection during the compression stroke needs high pressure hydrogen and thus effectively requires liquid hydrogen storage (metal hydrides can only provide low pressure hydrogen, compressed hydrogen could be used but this limits the effective tank contents as the tank can only be emptied down to the fuel injection pressure) [13]. Simulation and Optimization of a Hydrogen Internal Combustion Engine 23 2.8. Problems of hydrogen combustion For many years hydrogen combustion engines have been studied although the major number of published papers appeared during and in the years following the oil crises. The main difficulties on developing H2ICE’s and the consequences of it will be now summarized in this section [21]. 2.8.1. Abnormal combustion The same properties that make hydrogen an attractive fuel, wide flammability limits, low required ignition energy and high flame speeds, are also the ones who can result in undesired combustion phenomena. Controlling abnormal combustion is very important for the engine design, mixture formation and load control, although it has been a challenge to control it. Backfire can, in the best scenario, make the engine stop as the fuel is consumed before it can enter the cylinders and deliver work, while in the worst scenario, it can lead to the destruction of the intake manifold. The effects of pre-ignition and knock can go from increasing noise and vibration to major engine damage [8]. 2.8.1.1. Backfire Backfire occurs during the opening of the intake valves while the new air-hydrogen mixture is aspired into the combustion chamber. It can be named differently depending on the authors: backflash, flashback and induction ignition. The main difference between backfiring and pre-ignition is the timing at which the anomaly occurs. Pre-ignition takes place during the compression stroke with the intake valves already closed, whereas backfiring occurs with the intake valves still open [8]. Many are the causes pointed for backfire such as:  Hot spots in the combustion chamber (deposits and particulates, the spark plug, residual gas, exhaust valves, etc.);  The small quenching distance of hydrogen (together with the wide flammability limits), enables the flame to propagate in the piston top, travelling up to inlet valve and igniting the fresh charge;  Remaining energy in the ignition circuit that was not totally discharged within the flame can cause a second, unwanted, ignition while the intake or expansion stroke occur (pressure is low);  Pre-ignition rises the temperature of the chamber, causing a hot spot that leads to a first pre-ignition which increases temperature, resulting in another, earlier, pre-ignition in the next cycle, leading to a new hot spot, and so on. Simulation and Optimization of a Hydrogen Internal Combustion Engine 24 All causes itemized above can indeed result in backfire and the design of a hydrogen engine should try to avoid them. Many researches have been done showing that, even eliminating or avoiding the main supposed causes as hot spots, backfire still occurs. Even though, it is important to avoid them as they can lead to pre-ignition which increases the engine’s thermal loading and can have detrimental effects even without leading to backfire [8; 9]. 2.8.1.2. Pre-ignition The actual reason or cause why pre-ignition occurs has never been proven, although many hypotheses haven been proposed to explain it. Besides hydrogen characteristics, high temperatures, residual charge, engine speed and engine load can cause pre-ignition. Also, due to the dependence of minimum ignition energy with the equivalence ratio, pre-ignition is more pronounced when the airhydrogen mixtures approach stoichiometric levels [12; 13]. 2.8.1.3. Auto-ignition / Knock Engine knock is the term used in spark ignition engines to describe auto-ignition of the remaining end-gas during the late part of the combustion event with high-pressure oscillations and the typical pinging noise. The proportions of engine damage depend on the amplitude of the pressure waves and the subsequent increased mechanical and thermal stress. The engine knock depends on the engine design and the fuel-air mixture properties. At high loads, knock is a more significant source of efficiency losses than pumping work. Knock is the spontaneous ignition of part of the charge. This can lead to excessively high cylinder temperatures and pressures as well as objectionable noise. Knock is addressed in a number of different ways in engines, including reducing the compression ratio and retarding spark timing. The global effects of knock and pre-ignition are very similar, and on occasion there are some literature texts that do not differentiate them. However, the way to prevent each is different: pre-ignition can be avoided through proper engine design, on the other hand knock is an inherent limit on the maximum compression ratio that can be used with a fuel [8]. 2.9. Safety Safety is one of the most important issues when trying to implement hydrogen vehicles for common use. It is also essential to those who work with hydrogen in production, transportation and research. Regarding the physical properties of hydrogen, the fundamental safety dealing with hydrogen lies on its potential to ignite or explode, especially in indoor areas. The process of detonation starts when the flame front changes from laminar to turbulent structure. The flame speed accelerates caused by preheating pressure of the unburned gas mixture and shock waves. Detonation can happen to any other gaseous fuels, although hydrogen presents much higher burning velocity than the other fuels, 200 cm/s and 40-80 cm/s, respectively. In section 2.5. the options of storing hydrogen on board were presented. Under normal conditions, the storage and fuel lines should keep hydrogen and air separate so as to avoid flammable or Simulation and Optimization of a Hydrogen Internal Combustion Engine 25 detonable mixtures. This requires maintaining an intact and leak-free hydrogen storage and delivery system. This can be achieved by using appropriate materials and good quality of construction. Taking in consideration that hydrogen is more propitious of passing through small openings than other gaseous fuels, a higher quality of construction is needed to minimize small cracks and defects that could grow and lead to hydrogen leakage. Operation with hydrogen should be done outdoors as much as possible. When hydrogen operations are indoor, the space should be very well ventilated to avoid the formation of flammable or detonable fuel-air mixtures. This puts a limitation for vehicles to be parked in garage for a long period. Hydrogen sensors are seen as devices for facilitating the detection of unwanted hydrogen leaks and to prevent eventual accidents. In the presence of hydrogen, sensors are activated sounding an audible alarm, or activating the ventilation systems or shutdown the hydrogen systems to a safe stand-by state [36; 37]. 2.10. Hydrogen combustion engine vehicle The early history of H2ICE vehicles dates back to 1807 when Francois Isaac de Rivaz of Switzerland built the first working model that used a mixture of hydrogen and oxygen as a reactant. Since then, institutions, mainly automotive companies, have been developing and improving the technology, searching for a more sustainable and clean fuel source [38]. 2.10.1. Characterization H2ICE’s vehicles can be distinguished by the purpose they are built for. If a vehicle is specifically designed and built for hydrogen operation by an original equipment manufacturer, then is a dedicated vehicle. On the other hand, if the vehicle is adapted for hydrogen operation by either a manufacturer or an aftermarket supplier is a conversion vehicle. The properties of hydrogen, in particular its wide flammability limits, make it an ideal fuel to combine with other fuels and thereby improve their combustion properties. In this sense, the vehicles can be built for mono-fuel operation with hydrogen, as the only fuel, as well as bi-fuel solutions, with hydrogen as well as other fuel. Based on the mixture formation strategy, one can differentiate between:  Blended operation, the combinations of hydrogen with one or several other gaseous fuels;  Dual-fuel operation describes any combination of hydrogen and liquid fuels in which several mixture preparation devices are used. These systems use separate storage and fuel systems for the different fuels. Concerning the hydrogen onboard storage system, hydrogen vehicles can be grouped as compressed hydrogen and cryogenic liquid hydrogen vehicles. Simulation and Optimization of a Hydrogen Internal Combustion Engine 32 1Hydrogen bottle 2Ball valve 3Electromagnetic cut-off valve 4First pressure reducing valve (13 MPa/0.8 MPa) 5Filter 6Hydrogen flow meter (CMF010) 7Hydrogen flow meter (CMF025) 8Second pressure reducing valve (0.2-0.5 MPa) 9Back-fire relief valve 10Air Filter 11Air flow meter 12Steady gas box 13Hydrogen injectors 14Turbine flow meter 15Three-way catalytic converter 16AVL exhaust analyzer sampling channel 17Computer analysis Figure 19 - Diagram of hydrogen internal combustion engine rig The test cell included a CW250 eddy current dynamometer, which was used for energy absorption and engine speed regulation. The dynamometer had a capacity of 250 kW and a maximum rated speed of 8000 rpm and was attached to an external blower, with volume flow rate of 500 m3/h. The engine speed could be controlled at the desired level, and the torque was varied. The speed, engine oil temperature, coolant temperature, and intake air temperature were recorded automatically from the dynamometer control console. The cylinder pressure was measured using a Kislter 6117B pressure sensor, and the crank angle position was specified by the crank angle encoder, which type is Kislter 2613B (which can measure 0-20000r/min and the accuracy can reach to 0.1 °CA – crank angle). The cylinder pressure and the corresponding crank angle were captured through a high-speed data acquisition system (Kibox Simulation and Optimization of a Hydrogen Internal Combustion Engine 33 combustion analyzer). The output from these measurements were diagrams of pressure versus crank angle. The inlet air flow was measured by a ToCeiL20N hot-film air mass flow meter. The hydrogen mass flow was measured by an EMERSON Coriolis mass flow meter, type CMF025. All the specifications were listed in table 4. Table 4 - Specification of experimental variables Variable Device Accuracy Parameters 2600rpm, WOTa Error Average of uncertainty (%) Engine speed FC2000 ±1r/min Brake power 28.1668 0.0574% 0.20 Crank angle Kislter 2613B ±0.02° ITEb 32% 0. 07% 0.23 In-cylinder pressure Kislter 6117B ±0.4% ARa ISFCb 93.7450 0.2127 0.23 Air mass flow rate ToCeiL20N ±1%FSa Volumetric efficiency 83.27% 0. 77% 0.92 Hydrogen mass flow rate CMF025 ±0.1%FSa Equivalence ratio 0.5170 0.0026 0.51 a FS: Full scale, AR: All range, WOT: wide open throttle. b ITE: Indicated Thermal Efficiency, ISFC: Indicated Specific Fuel Consumption. Before conducting any test, the engine is warmed up to ensure that it reaches the operating temperatures and that it stabilizes. Tests were conducted after running the engine until it reached a steady state oil temperature of 90 °C and cooling water temperature of 80 °C. The data was then recorded after running the engine with hydrogen fuel. All the tests were run at the MBT to obtain comparable data. The MBT tests were done through modifying the ignition timing at different engine speeds and loads. For example, to get the MBT at 2600 rpm and the wide open throttle, the engine speed should be kept at 2600 rpm and the throttle was wide open, modifying the hydrogen mass flow to keep the equivalence ratio at a constant value (such as 0.55). After these steps, the ignition timing was modified, through the electronic system. The test data were recorded until finding the MBT. The above steps were repeated in order to get the other test data at different speeds, equivalence ratios and throttle open angles. All measurements of physical quantities have some degree of uncertainty, due to various sources. Therefore, uncertainty analysis was necessary, to confirm the precision of the tests. The uncertainty for the experimental results was determined according to the principle of root-mean square method, to get the magnitude of the error given by Gaussian distribution, as follows: ∆𝑅=⌈(𝜕𝑅 𝜕𝑥1∆𝑥1)2+(𝜕𝑅 𝜕𝑥2∆𝑥2)2+⋯+(𝜕𝑅 𝜕𝑥𝑛∆𝑥𝑛)2⌉1/2 (3.8) Simulation and Optimization of a Hydrogen Internal Combustion Engine 34 where ∆R is the uncertainty in the computed result, R is a given function of the computed results, x1, x2, xn are the independent measured variables, ∆x1, ∆x2, ∆xn are the corresponding uncertainty values of the independent measured variables. Table 4 summarizes the average uncertainties of the measured parameters based on the specification of the instruments and experimental error analysis. The error analysis was performed by considering error rates in the measurement range of devices (according to their calibration values) used in the experimental studies. 3.4.1. Adaptations from the gasoline model to the hydrogen model The engine used in the experiments was adapted from gasoline. So some adjustments had to be made in order to make it work with the best efficiency using hydrogen as a fuel. The intake, exhaust, spark, and hydrogen supply system all suffered modifications, as well as the controlling system. In the same way, when using the software to design the hydrogen and gasoline models for the same engine there are many parameters that need to be changed. The form factor of the Wiebe function m, will be considered as 1.5 for the hydrogen model, while the normal value for a gasoline engine is 2.0. This difference is due to the higher burning speed of hydrogen compared to gasoline. As seen, in the properties of hydrogen section, the fuel/air ratio for hydrogen is much smaller than for the other fuels. In the experimental part, fluctuations in the equivalence ratio will be set in order to analyze the engine break power. Simulation and Optimization of a Hydrogen Internal Combustion Engine 35 [Blank Page] Simulation and Optimization of a Hydrogen Internal Combustion Engine 36 4. Measurements, results and discussion 4.1. Changes in duct intake dimensions In this section are analyzed the best relations of diameter and length of the intake duct, in order to have the highest MBT results. As stated before, the engine suffered some adaptations to work with hydrogen, although, the intake duct was kept as the original for the gasoline setup. The original intake duct dimensions are in table 5. Using WAVE software it was analyzed which should be the ideal diameter and length for the intake duct using hydrogen as a fuel. The simulation results are presented below in figures 20 and 21. Table 5 - Original intake duct dimensions Diameter (mm) Length (mm) 44 100 4.1.1. Diameter The engine was simulated for three different engine speeds, low 2400 rpm, medium 3600 rpm and high 4800 rpm. The graphic of the figure 20 correlates the duct diameter with the engine break torque. Figure 20 - Relation between brake engine torque and intake duct diameter for different engine speeds Figure 20 shows that for lower speeds the diameter of the intake duct does not affect much the engine brake torque, as this parameter is almost constant. For the higher engine speed of 4800 rpm the change of the intake duct makes the torque decrease for values over 40 mm of diameter. For diameters between 35 and 40 mm the torque value is slighting increasing reaching its maximum for 40 mm diameter. 110 120 130 140 150 160 170 180 190 35 36 37 38 39 40 41 42 43 44 45 46 Engine brake torque (N.m) Intake duct diameter (mm) 2400 rpm 3600 rpm 4800 rpm Simulation and Optimization of a Hydrogen Internal Combustion Engine 37 Table 6 - Analysis of different values of diameter and respective MBT response Diameter [mm] MBT 2400 rpm [N.m] MBT 3600 rpm [N.m] MBT 4800 rpm [N.m] Average [N.m] 35.4 114.2 127.6 181.7 141.2 38.6 114.0 127.0 182.8 141.3 40 114.3 127.0 184.6 142.0 44 113.5 126.2 172.1 137.3 46 113.2 126.0 172.1 137.1 The original diameter used was 44 mm. The simulation results, specified in table 6, show that the best compromise between torque and intake duct diameter is for values between 35.4 mm to 40 mm. 4.1.2. Length Figure 21 shows how the intake duct length changes the engine brake torque. Figure 21 - Relation between brake engine torque and intake duct length When the engine is running at 2400 rpm and 3600 rpm the engine torque does not suffer much change with the variation of the intake duct. On the other hand, when running the engine at 4800 rpm, longer intake ducts result in higher engine brake torques. In this sense it is important to find the best relation, as the engine is supposed to run at different speed conditions and should have the best relation of torque/dimensions. 110 120 130 140 150 160 170 180 190 200 50 60 70 80 90 100 110 120 130 Engine brake torque (N.m) Duct length (mm) 2400 rpm 3600 rpm 4800 rpm Simulation and Optimization of a Hydrogen Internal Combustion Engine 38 Table 7 - Analysis of different values of intake duct length and respective MBT response Length [mm] MBT 2400 rpm [N.m] MBT 3600 rpm [N.m] MBT 4800 rpm [N.m] Average 50 114.6 127.5 171.1 137.7 70 113.5 127. 4 172.0 137.6 90 113.5 126.2 171.3 137.0 110 113.6 126.0 191.0 143.5 130 113.5 128.1 180.4 140.7 Analyzing the results, table 7, it is possible to notice that the brake engine torque for the 2400 rpm simulation suffers small changes ( 1.3 N.m) when compared to 4800 rpm simulation ( 23 N.m). The 110 mm length offers the best relation. 4.2. Optimized the valve timing for the mean brake torque Adjusting the valve timing to the characteristics of the fuel in use, achieves better efficiency results. Accordingly, this section is focused in evaluating the influence of valve timing upon the corresponding brake torque. The opening and closing times of both intake and exhaust valves will be analyzed. 4.2.1. EVO – Exhaust Valve Opening time The engine is set up to open the exhaust valve at 126.36 degrees of the crank angle. In this simulation it was verified the influence of different opening timings on the respective brake torque. Figure 22 - EVO timing relation with brake torque 95 105 115 125 135 145 155 165 175 185 195 110 120 130 140 150 Brake engine torque (N.m) Exhaust Valve Opening (deg) 2400 rpm 3600 rpm 4800 rpm Simulation and Optimization of a Hydrogen Internal Combustion Engine 39 The 2400 rpm simulation results in low torques for early valve opening, continuing to grow until 130 degrees of EVO and keeping more or less constant until 150 degrees of EVO. For the 3600 rpm there is a continuous grow until reaching the peak at 145 degrees and decreasing abruptly after that. The higher engine speed simulation presents a continuous growth of torque with the delaying of EVO, although with some small peaks for certain values. It presents its maximum also for 145 degrees of EVO, figure 22. In this sense, with the data from the software an average timing was determined to conclude which value was the best torque compromise for both engine speeds, table 8. Table 8 - EVO timing results and interpolation analysis EVO [deg] MBT 2400 rpm [N.m] MBT 3600 rpm [N.m] MBT 4800 rpm [N.m] Average [N.m] 110 102.7 126.1 167.8 132.2 115 109.5 122.8 173.7 135.3 120 111. 3 123.7 170.3 135. 1 130 113.9 128.1 172.6 138.2 135 113.7 131.7 177.4 141.0 140 113.2 140.5 176.8 143.5 145 112.8 151.9 182.1 148.9 150 112.6 129.5 175.3 139.1 From the WAVE software study and subsequent interpolation from the obtained torque values, table 8, the new suggested value for the EVO timing was 145 degrees. This represents the best compromise for all speed cases. 4.2.2. EVC – Exhaust Valve Closing time The engine is set up, for the exhaust valve, to have a duration of exhaust phase (represented as a function of the crank angle position) of 1.0. Keeping the EVO set as 126.36 degrees of the crank angle and changing the duration of the valve opening is possible to obtain the exhaust valve closing time with respective brake engine torque response, figure 23. The new EVC timing is calculated by the WAVE software like, the equation: 𝐸𝑉𝐶𝑛𝑒𝑤 =𝐸𝑉𝐶∗ 𝑑𝑢𝑟𝑎𝑡𝑖𝑜𝑛 (4.1) Being the EVC calculated automatically by the software for any engine as, 𝐸𝑉𝐶=𝐸𝑉𝑂+ 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝑣𝑎𝑙𝑢𝑒 (4.2) This constant value is based on the data of the table 18, annex G. Simulation and Optimization of a Hydrogen Internal Combustion Engine 40 Figure 23 - EVC timing relation with brake torque The graphics from figure 23 have similar distributions, presenting low torque values for early closing valve time (short duration) and keep increasing their values until reaching its maximum at duration of 1.0 for 2400 rpm, 0.9 for 3600 rpm and 0.95 for 4800 rpm. Once again, in table 9, are presented averages of the torque values to get the best operating compromise. Table 9 - EVC timing results and interpolation analysis Duration MBT 2400 rpm [N.m] MBT 3600 rpm [N.m] MBT 4800 rpm [N.m] Average [N.m] 0.85 75.5 97.5 144.9 106.0 0.9 94.4 138.0 177.2 136.5 0.95 109.3 123.4 179.9 137.5 1 113.5 126.2 172.1 137.3 1.05 112.5 134.8 167.5 138.3 1.1 109.4 133.2 167.8 136.8 The obtained data show that values of EVC can be very wide, presenting very similar torque responses between 136 and 138 N.m. However, 1.05 is the one that presents the higher torque value and so it should be considered for future testing. 4.2.3. IVO – Intake Valve Opening time The engine is set up to open the intake valve at 336.7 degrees of the crank angle. In this simulation different opening timings were considered and the respective brake torque values, figure 24, were obtained. 70 90 110 130 150 170 190 0,85 0,9 0,95 1 1,05 1,1 Brake engine torque (N/m) Duration 2400 rpm 3600 rpm 4800 rpm Simulation and Optimization of a Hydrogen Internal Combustion Engine 41 Figure 24 - IVO timing relation with brake torque The curve representing the 2400 rpm engine speed simulation has a continuous growth from 320 till 350 degrees. On the other hand, for the middle engine speed the brake torque decreases from 325 till 350 degrees, having its peak at 325 degrees. For the highest engine speed there are many variations in the torque results through all IVO values, having two peaks for IVO at 320 degrees and 335 degrees. Because these graphics present very different patterns, it is difficult to make a proper analyze of what is the best IVO timing. Once again, using the data from the software, an analysis was made to find out the best compromise of torque for the tested engine speeds, table 10. Table 10 - IVO timing results and interpolation analysis IVO [deg] MBT 2400 rpm [N.m] MBT 3600 rpm [N.m] MBT 4800 rpm [N.m] Average [N.m] 320 108.6 138.0 196.1 152.4 325 110.96 145.4 177.4 144.2 330 115.2 132. 3 176.1 145.6 335 113.2 127.6 191.9 152.5 340 115.3 124.1 174.4 144.8 345 115.5 122.9 184. 1 149.8 350 114.1 121.6 180.2 147.2 The results show that the IVO timing that presents the best torque is at 335 degrees. As the engine was tested with an IVO time very close (336.7 degrees) to this value, analyses with shorter increments of IVO were made and the results are presented in table 11. 100 110 120 130 140 150 160 170 180 190 200 320 325 330 335 340 345 350 Brake engine torque (N/m) Intake Valve Openning (deg) 2400 rpm 3600 rpm 4800 rpm Simulation and Optimization of a Hydrogen Internal Combustion Engine 48 5. Conclusions The production of hydrogen is still the major issue to solve if this technology is to become part of the market at prices competitive with other fuels. Besides that, the major source to obtain hydrogen is carbon based extraction, with high carbon dioxide emissions, and so the hydrogen cannot be considered a clean energy carrier. Clean systems of hydrogen extraction should be developed in order to be more efficient and less polluting and maybe making hydrogen a possible reference fuel in the near future. Hydrogen storage is still in phase of development in order to get the best volume to weight ratio. There are many new suggested technologies that need more research to make them into use. Compressed hydrogen seems to be for now the best on-board solution. Regarding delivery process, systems are not fully developed because there is no market that demands for it. Once demand grows, different solutions that have been presented, can eventually be adopted. Problems regarding hydrogen combustion are frequent although the causes are not yet totally defined. Safety procedures are well stablished and if followed no incidents for the users should happen. The existent hydrogen combustion fueled vehicles are not yet available for commercial sale and only a few prototypes have been built. There are many drawbacks, namely with the evolution of the electric car. Many companies are forgetting the idea of hydrogen fuel for combustion engines as a possible future technical solution. For the engine used in the practical experiments, it was found that a longer length and smaller dimeter for the intake duct would give higher brake torque. Also new values for the opening and closing valves timings were suggested to achieve higher torque response from the engine. As the new parameters suggested to be used for the engine, were taken based on previous parameters, it is an iteration process to leads to the ideal solution. New recommended values for the combustion time and throttle angle were also proposed in order to get higher engine torque response. The simulation of the EGR model showed that the implementation of this in the real engine could bring benefits in terms of reducing NOx emissions without compromising much the brake engine torque. Simulation and Optimization of a Hydrogen Internal Combustion Engine 49 [Blank Page] Simulation and Optimization of a Hydrogen Internal Combustion Engine 50 6. Recommendations for future work In order to evaluate the new suggested intake duct dimensions, the original one should be replaced by a new duct with the suggested dimensions and new engine operating data acquired. For the optimized opening and closing valve timing, it would be interesting to check what would be the final torque result if of all parameters were changed to the suggested values. Since each of the new timings was taken keeping the other timings constant, a final testing considering the combination of the proposed changes is recommended. The proposed EGR model should be implemented and tested in the engine and new values of NOx emissions and brake engine torque experimentally determined. For all parameters considered in this simulation, only the engine brake torque response was evaluated as a decision factor. For future studies it would be adequate to consider other output parameters such as NOx emissions or engine efficiency. The same analyzes should also be carried out for a larger range of engine speeds. Finally, it must be stressed that this combined experimental and numerical evaluation is an iteration process, taking values from the engine, simulating in software, analyzing the numerical results, testing them in the engine and going through this sequence all over again. 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Richtář, "Simulataion Model of the Single Cylinder Combustion Engine MZ125," VŠB - Technical University of Ostrava, Prague, Check Republic, 2011. [46] A. J. Torregrosa and P. C. Olmeda, "Revisng Engine Heat Transfer," Journal of Engineering of the University of Hunedoara, p. 21, 2008. [47] M. Amin and Y. Wenming, "An advanced combustion model coupled with detailed chemical reaction mechanism for D.I diesel engine simulation," Applied Energy, vol. 111, pp. 758-770, 2013. [48] T. Alger, "Cooled EGR improves fuel economy and emissions in gasoline engines," Technology Today, p. 4, 2010. Simulation and Optimization of a Hydrogen Internal Combustion Engine 55 Annexes A. Fuel cost estimates with oil at USD 60/bbl, fixed feedstock prices and no oil price affects other input costs Figure 30 - Near and long term comparative cost analysis of production of different fuels Simulation and Optimization of a Hydrogen Internal Combustion Engine 56 B. Engine Model diagram B.1. Basic engine diagram Figure 31WAVE software hydrogen engine model B.2. Engine Diagram with EGR system Figure 32 - WAVE software hydrogen engine model with EGR system Simulation and Optimization of a Hydrogen Internal Combustion Engine 57 C. Cylinder block and head temperature Table 14 presents the simulation values for the cylinder block and head temperature in function of the power. Table 14 - Cylinder block and head temperature Head Piston Liner Power [kW] Temperature [K] Temperature [K] Temperature [K] 10 413.15 453.15 373.15 20 423.15 463.15 378.15 40 443.15 483.15 383.15 60 455.15 495.15 388.15 80 465.15 505.15 393.15 100 473.15 513.15 398.15 120 481.15 521.15 403.15 140 493.15 533.15 408.15 160 503.15 543.15 413.15 180 513.15 553.15 418.15 Simulation and Optimization of a Hydrogen Internal Combustion Engine 64 Table 19 presents the cam profile for the intake phase based on the engine testing values. Table 19 - Cam profile for the exhaust phase Exhaust Crankangle [°CA] Lift [mm] Crankangle [°CA] Lift [mm] Crankangle [°CA] Lift [mm] 0.00000 126.36 0.00000 6.62570 268.36 8.14901 0.02688 378.36 0.09521 0.00708 128.36 0.00651 6.57359 270.36 8.09968 0.01814 380.36 0.08129 0.01392 130.36 0.01197 6.51611 272.36 8.04380 0.01228 382.36 0.06887 0.02378 132.36 0.01908 6.45326 274.36 7.98140 0.00849 384.36 0.05787 0.03723 134.36 0.02849 6.38506 276.36 7.91249 0.00577 386.36 0.04821 0.05524 136.36 0.04108 6.31153 278.36 7.83709 0.00000 388.36 0.03982 0.08227 138.36 0.05905 6.23271 280.36 7.75521 390.36 0.03260 0.12461 140.36 0.08733 6.14860 282.36 7.66689 392.36 0.02649 0.18856 142.36 0.13180 6.05925 284.36 7.57214 394.36 0.02141 0.27959 144.36 0.19708 5.96467 286.36 7.47099 396.36 0.01726 0.39895 146.36 0.28592 5.86490 288.36 7.36347 398.36 0.01398 0.54559 148.36 0.39958 5.75997 290.36 7.24962 400.36 0.01147 0.71425 150.36 0.53814 5.64991 292.36 7.12945 402.36 0.00966 0.89861 152.36 0.70057 5.53474 294.36 7.00300 404.36 0.00000 1.09238 154.36 0.88485 5.41452 296.36 6.87032 1.28940 156.36 1.08824 5.28928 298.36 6.73143 1.48654 158.36 1.30749 5.15905 300.36 6.58637 1.68368 160.36 1.53912 5.02388 302.36 6.43519 1.88083 162.36 1.77972 4.88381 304.36 6.27793 2.07797 164.36 2.02608 4.73888 306.36 6.11463 2.27512 166.36 2.27540 4.58914 308.36 5.94534 2.47226 168.36 2.52534 4.43463 310.36 5.77010 2.66940 170.36 2.77404 4.27540 312.36 5.58897 2.86643 172.36 3.02012 4.11150 314.36 5.40199 3.06088 174.36 3.26258 3.94299 316.36 5.20922 3.25105 176.36 3.50077 3.76991 318.36 5.01072 3.43687 178.36 3.73426 3.59232 320.36 4.80655 3.61827 180.36 3.96279 3.41027 322.36 4.59675 3.79522 182.36 4.18622 3.22383 324.36 4.38141 3.96763 184.36 4.40443 3.03303 326.36 4.16061 4.13549 186.36 4.61735 2.83800 328.36 3.93449 4.29871 188.36 4.82490 2.64090 330.36 3.70327 4.45726 190.36 5.02701 2.44376 332.36 3.46729 4.61108 192.36 5.22362 2.24661 334.36 3.22706 4.76013 194.36 5.41466 2.04947 336.36 2.98335 4.90436 196.36 5.60005 1.85232 338.36 2.73718 5.04373 198.36 5.77975 1.65519 340.36 2.48992 5.17819 200.36 5.95369 1.45804 342.36 2.24332 5.30769 202.36 6.12181 1.26090 344.36 1.99949 5.43222 204.36 6.28405 1.06524 346.36 1.76088 5.55171 206.36 6.44037 0.87665 348.36 1.53026 5.66613 208.36 6.59071 0.70143 350.36 1.31055 5.77546 210.36 6.73502 0.54588 352.36 1.10474 5.87964 212.36 6.87325 0.41605 354.36 0.91569 5.97866 214.36 7.00536 0.31451 356.36 0.74599 6.07249 216.36 7.13130 0.24088 358.36 0.59772 6.16109 218.36 7.25104 0.19085 360.36 0.47229 6.24443 220.36 7.36453 0.15816 362.36 0.37037 6.32249 222.36 7.47173 0.13649 364.36 0.29171 6.39525 224.36 7.57262 0.11955 366.36 0.23478 6.46268 226.36 7.66715 0.10306 368.36 0.19569 6.52475 228.36 7.75531 0.08657 370.36 0.16827 6.58147 230.36 7.83705 0.07008 372.36 0.14681 6.63279 232.36 7.91235 0.05392 374.36 0.12789 6.67872 234.36 7.98119 0.03900 376.36 0.11072 Simulation and Optimization of a Hydrogen Internal Combustion Engine 65