Enginee ing and Technology Jou nal e-ISSN: 2456-3358
Volume 10 Issue 10 Oc obe -2025, Page No.-7274-7278
DOI: 10.47191/e j/ 10i10.07, I.F. – 8.482
© 2025, ETJ
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ETJ Volume 10 Issue 10 Oc obe 2025,
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Fa oug-Musaab O. El
Compa a i e S a egies o Nox Reduc ion in Diesel Engines
Musaab O. El-Fa oug1*, A i Ismail Adam Bash 2
1Elimam Elmahdi Uni e si y, Facul y o Enginee ing, Mechanical Enginee ing Depa men , Kos i, Sudan
2Kos i Technical College, Mechanical Enginee ing Depa men , Kos i, Sudan
ABSTRACT: This s udy in es iga es he educ ion o ni ogen oxide (NOx) emissions in diesel engines using compu a ional
simula ions pe o med wi h Diesel-RK. Th ee in-cylinde con ol s a egies we e e alua ed: exhaus gas eci cula ion (EGR),
di ec wa e injec ion, and a ia ions in combus ion chambe dep h. Simula ions we e conduc ed on a six-cylinde , ou -s oke
diesel engine a engine speeds anging om 1000 o 3000 pm. The esul s show ha inc easing EGR lowe s NOx emissions by
educing peak combus ion empe a u es h ough oxygen dilu ion and enhanced mix u e hea capaci y. Wa e injec ion was ound
o be he mos e ec i e s a egy, educing NOx o nea ly negligible le els ac oss all speeds by combining e apo a i e cooling,
hea abso p ion, and oxygen displacemen . Changes in combus ion chambe dep h had a mode a e in luence, wi h shallowe
chambe s imp o ing swi l and mixing, he eby lowe ing local empe a u e peaks and supp essing NOx o ma ion. O e all, he
indings highligh wa e injec ion as he mos e ec i e s andalone s a egy, while combining i wi h op imized chambe geome y
and mode a e EGR o e s a p omising in eg a ed app oach o NOx con ol in diesel engines.
KEYWORDS: Diesel engine, RK-diesel, NOx emission, Op imiza ion
I. INTRODUCTION
Global popula ion g ow h, economic expansion, and
u baniza ion ha e d i en inc eased eliance on in e nal
combus ion (IC) engines, which a e widely used in
au omobiles, po able machine y, and locomo i es due o
hei high powe - o-weigh a io and compac size [1].
Cu en ly, o e 600 million ehicles ope a e wo ldwide.
Howe e , IC engines emi pollu an s such as NOx, CO, CO₂,
hyd oca bons, and pa icula e ma e , posing signi ican
en i onmen al and heal h isks.
NOx o ma ion is s ongly in luenced by combus ion
empe a u e, esidence ime o high- empe a u e gases,
oxygen a ailabili y, and u bulence [2]. Longe exposu e o
bu n gases o high empe a u es and p essu es p omo es
NOx p oduc ion, pa icula ly in low-speed engines.
Tu bulence accele a es uel-ai mixing, inc easing eac ion
a es. Techniques o educe peak combus ion empe a u es
can lowe NOx bu may a ec o he emissions and engine
pe o mance, o en esul ing in a uel penal y. No single
s a egy e ec i ely op imizes bo h emissions and
pe o mance.
To mi iga e hese e ec s, go e nmen s ha e implemen ed
s ingen emission s anda ds, including Eu o s anda ds in
Eu ope, EPA s anda ds in he USA, and Japanese
egula ions, wi h Eu o 6 in oduced in 2014 and Eu o 7
planned by 2025. Policies also p omo e eco- iendly
ehicles and ea ly e i emen o olde diesel engines,
alongside ad anced a e - ea men echnologies, o educe
NOx emissions and hei en i onmen al impac [3].
Exhaus Gas Reci cula ion (EGR) is an e ec i e and
economical s a egy o educe NOx by lowe ing peak
combus ion empe a u es h ough eci cula ing pa o he
exhaus in o he in ake, which educes oxygen concen a ion
[4]. Banglin e al. [5] epo ed ha EGR nea ly hal ed NOx
emissions and educed PM and PN, wi h minimal impac on
uel consump ion and sligh e iciency gains. Howe e ,
highe HC and CO emissions occu ed due o combus ion
de e io a ion, highligh ing he ade-o s be ween emission
con ol and engine pe o mance. Deng e al. [5] epo ed ha
EGR a e signi ican ly a ec s diesel engine he mal
e iciency. Expe imen s wi h a wo-s age u bocha ged
engine showed dis inc ends be ween 0–18% and 18–51%
EGR, wi h o al inpu ene gy and in ake en halpy as he
main ac o s in luencing e iciency. Hu e al. [6] used CFD
o s udy EGR in me hanol- ueled ma ine engines, inding
ha while NOx was educed by up o 65%, high EGR
ex ended igni ion delay, combus ion du a ion, and lowe ed
cylinde p essu e. Rajesh Kuma and Sa a anan [7]
obse ed maximum NOx educ ions o 27–35% wi h 30%
EGR, bu highe soo , HC, and sligh CO inc eases occu ed
due o educed oxygen a ailabili y, highligh ing he ade-
o s be ween emissions and combus ion pe o mance.
Muhammad e al. [8] e iewed 204 s udies (1958–2024) on
wa e injec ion in diesel engines, iden i ying Di ec Wa e
Injec ion (DWI), Emulsion Injec ion, and In ake Mani old
Wa e Injec ion (IMWI) as main me hods. Emulsion and
IMWI we e a o ed o equi ing minimal engine
modi ica ion. Wa e injec ion imp o ed b ake he mal
e iciency by 10–15%, educed BSFC by 5–10%, and cu
“Compa a i e S a egies o Nox Reduc ion in Diesel Engines”
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Fa oug-Musaab O. El
emissions (up o 60% NOx, ~25% PM, 10–20% CO/CO₂),
wi h emulsion injec ion o e ing he bes balance be ween
pe o mance and emission educ ion. Ahmad e al. [9]
epo ed ha wa e -diesel emulsions (5–20% wa e , 2%
su ac an ) enhanced uel e iciency and educed NOx and
PM, hough CO and CO₂ inc eased unde speci ic loads. The
E20 blend showed in-cylinde p essu es compa able o
diesel wi h highe hea elease, con i ming emulsions as a
iable s a egy o imp o ing e iciency and lowe ing
emissions. Sun e al. [10] showed ha Di ec Wa e
Injec ion (DWI) du ing he comp ession s oke can educe
NOx emissions by up o 55.6% by lowe ing lame
empe a u es h ough wa e e apo a ion. Howe e , his
app oach may sligh ly inc ease pa icula e ma e (PM) and,
a highe wa e le els, CO and unbu ned hyd oca bons
(HC). Zhangming e al. [11] s udied wa e po injec ion in
diesel/me hane dual- and i- uel engines. Me hane educed
combus ion in ensi y and delayed igni ion, while wa e
u he delayed combus ion. Combined injec ion no ably
dec eased NOx and PM, hough CO and HC inc eased. The
esul s indica e ha wa e and me hane injec ion oge he
can e ec i ely mi iga e bo h NOx and pa icula e emissions.
In his s udy, compu a ional simula ions we e pe o med
using Diesel-RK o analyze a diesel engine ope a ing on
con en ional diesel uel. The model in es iga ed he e ec s
o exhaus gas eci cula ion (EGR), wa e injec ion, and
combus ion chambe geome y on NOx emissions, aiming o
iden i y e ec i e s a egies o hei educ ion.
II. METHODOLOGY
DIESEL-RK is a comp ehensi e he modynamic simula ion
pla o m designed o ull-cycle analysis o in e nal
combus ion engines. The so wa e in eg a es ad anced
compu a ional models ha allow o de ailed examina ion o
combus ion dynamics, emission o ma ion p ocesses, and
s a egies o pe o mance op imiza ion. Ini ially de eloped
a Bauman Moscow S a e Technical Uni e si y be ween
1981 and 1982, DIESEL-RK has unde gone ex ensi e
de elopmen h ough mul iple e sions. Wha s a ed as a
ool ocused on combus ion op imiza ion has e ol ed in o a
obus simula ion en i onmen widely used in in e nal
combus ion engine esea ch and de elopmen . I s co e
ma hema ical amewo ks—including he RK-model o
sp ay dynamics and he Zeldo ich and de ailed kine ic
mechanisms o NOx p edic ion—ha e been ho oughly
alida ed ac oss di e se engine con igu a ions. Ongoing
enhancemen s, d i en by bo h indus ial and academic
demands, ha e added capabili ies such as mul ipa ame ic
op imiza ion algo i hms, uel sp ay isualiza ion ools, and
use - iendly in e ace wiza ds, making he pla o m sui able
o bo h p ac ical enginee ing applica ions and scien i ic
in es iga ions [12].
Accu a e uel physical p ope ies a e essen ial as inpu da a
o calcula ing sp ay dynamics, d ople size, and,
consequen ly, e apo a ion and hea elease a es. The
p ope ies o diesel uel used in his s udy a e summa ized in
Table 1.
Table 1: P ope ies o Diesel uel [13].
P ope y
Diesel
C Mass F ac ions (%)
0.87
H Mass F ac ions (%)
0.126
O Mass F ac ions (%)
0.004
Sul u F ac ion (%)
0
Low Hea ing Value (MJ/kg)
39
Appa en Ac i a ion Ene gy (kJ/mol)
23
Ce ane Numbe
48
Densi y a 323K (kg/m3)
830
Dynamic Viscosi y coe icien (Pa.s)
0.003
Molecula Mass
190
In his s udy, he o ma ion and educ ion o ni ogen oxide
(NOx) emissions om diesel combus ion we e in es iga ed
using compu a ional simula ion. Th ee di e en con ol
s a egies we e e alua ed o iden i y he mos e ec i e
app oach o minimizing NOx emissions: (i) exhaus gas
eci cula ion (EGR), (ii) di ec wa e injec ion, and (iii)
modi ica ion o he combus ion chambe dep h. The
nume ical simula ions we e ca ied ou on a six-cylinde ,
ou -s oke diesel engine, whose de ailed echnical
speci ica ions a e lis ed in Table 2. To ensu e a
comp ehensi e assessmen , engine pe o mance and
emission beha io we e analyzed unde i e dis inc
ope a ing speeds: 1000, 1500, 2000, 2500, and 3000 pm.
This app oach allowed o he e alua ion o he
e ec i eness o each me hod unde a ying ope a ing
condi ions, he eby p o iding a compa a i e basis o
op imizing NOx educ ion s a egies in diesel engines.
Table 2: De ails o he simula ion diesel engine.
Type
6L15/18
No. o Cylinde
6 in - line
Cooling Sys em
liquid
Cylinde Bo e (mm)
150
Pis on S oke (mm)
180
Cylinde Head Design
Fou al es
III. RESULTS AND DISCUSION
Figu e 1 depic s he e ec o exhaus gas eci cula ion
(EGR) on NOx emissions du ing diesel engine ope a ion.
The indings indica e ha highe EGR le els consis en ly
educe NOx emissions compa ed wi h baseline ope a ion
wi hou EGR. This educ ion is mainly associa ed wi h he
lowe ing o peak in-cylinde empe a u e, a dominan ac o
in NOx o ma ion, as highligh ed in ea lie esea ch [14].
In oducing eci cula ed exhaus gases in o he in ake cha ge
p oduces wo key ou comes: i s , a dilu ion o he oxygen
concen a ion, which slows he combus ion eac ions by
limi ing oxidize a ailabili y; and second, an inc ease in he
“Compa a i e S a egies o Nox Reduc ion in Diesel Engines”
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Fa oug-Musaab O. El
e ec i e hea capaci y o he cha ge, which dampens he
empe a u e ise o a gi en hea elease. Toge he , hese
e ec s supp ess he he mal NOx pa hways, ypically
desc ibed by he ex ended Zeldo ich mechanism, by
lowe ing he maximum combus ion empe a u e [15].
Consequen ly, highe EGR a es educe NOx emissions by
weakening combus ion in ensi y and dec easing peak in-
cylinde empe a u es [16].
Figu e1: Va ia ion o NOx emission wi h di e en EGR
a io
Figu e 2 illus a es he a ia ion o NOx emissions wi h
engine speed o a diesel engine ueled wi h con en ional
diesel and diesel–wa e blends con aining 10%, 20%, and
30% wa e . Fo he pu e diesel case, NOx emissions a e
ela i ely high a lowe engine speeds and p og essi ely
decline as speed inc eases, a end ha can be a ibu ed o
educed high- empe a u e esidence ime a highe speeds,
which limi s NOx gene a ion [2]. In con as , he addi ion o
wa e esul s in a sha p educ ion in NOx emissions, which
emain close o ze o ac oss he en i e speed ange. This
p onounced dec ease is p ima ily go e ned by h ee
mechanisms: (i) e apo a i e cooling om wa e
apo iza ion, which signi ican ly lowe s in-cylinde lame
empe a u es [17], (ii) he inc eased speci ic hea capaci y o
he cha ge, which dampens he empe a u e ise du ing
combus ion [18], and (iii) pa ial dilu ion o oxygen
concen a ion, which slows he oxida ion eac ions and
supp esses he mal NOx o ma ion h ough he ex ended
Zeldo ich mechanism [19]. Collec i ely, hese e ec s
demons a e he s ong po en ial o wa e –diesel blends in
mi iga ing NOx emissions compa ed wi h con en ional
diesel ope a ion.
Figu e2: Va ia ion o NOx emission wi h di e en wa e
a io
Figu e 3 p esen s he a ia ion o NOx emissions wi h
engine speed o a diesel engine ope a ing wi h di e en
combus ion chambe dep hs (d11, d13, d17, d20, and d23).
In all cases, NOx emissions a e highes a lowe engine
speeds and p og essi ely decline wi h inc easing speed,
app oaching app oxima ely 200 ppm a 3500 pm. Among
he chambe con igu a ions, he shallowes design
d11consis en ly yields he lowes NOx emissions, whe eas
deepe chambe s such as d20 and d23 end o p oduce highe
emissions, pa icula ly in he low-speed ange. This end
can be explained by he in luence o chambe geome y on
in-cylinde ai – uel mixing, u bulence in ensi y, and
combus ion empe a u e dis ibu ion. Shallow chambe s
p omo e enhanced swi l and mixing, esul ing in mo e
homogeneous combus ion and educed peak lame
empe a u es, he eby supp essing NOx o ma ion. In
con as , deepe chambe s localize combus ion in es ic ed
zones, leading o ele a ed peak empe a u es ha a o
he mal NOx gene a ion h ough he ex ended Zeldo ich
mechanism [20]. The o e all educ ion in NOx wi h
inc easing engine speed is consis en wi h he sho e high-
empe a u e esidence ime o combus ion p oduc s, which
cons ains NOx o ma ion despi e highe ope a ing loads
[21]. These obse a ions emphasize ha ca e ul
op imiza ion o combus ion chambe dep h is a iable design
app oach o imp o e mixing quali y, con ol empe a u e
dis ibu ion, and mi iga e emissions in diesel engines.
Figu e3: Va ia ion o NOx emission wi h di e en
combus ion chambe dep h
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Fa oug-Musaab O. El
Figu e 4 compa es h ee NOx educ ion s a egies wa e
injec ion, EGR, and a ia ions in combus ion chambe dep h
and highligh s he supe io e ec i eness o wa e addi ion.
Among he es ed me hods, wa e injec ion achie es he
g ea es educ ion, d i ing NOx emissions o nea ly
negligible le els ac oss all engine speeds. This s ong
pe o mance esul s om i s combined e ec s: e apo a i e
cooling ha lowe s in-cylinde lame empe a u es,
inc eased mix u e hea capaci y ha limi s empe a u e ise,
and pa ial oxygen dilu ion ha slows eac ion a es, all o
which supp ess he he mal NOx pa hway [22]. EGR also
educes emissions by dilu ing oxygen and inc easing
he mal capaci y o he in ake cha ge [23], while chambe
geome y adjus men s p o ide only mode a e bene i s by
in luencing swi l, mixing, and local empe a u e dis ibu ion
[24]. O e all, wa e injec ion is clea ly he mos e ec i e
s andalone echnique, and i s in eg a ion wi h op imized
chambe design and mode a e EGR could yield an e en
mo e obus NOx con ol s a egy o diesel engines.
Figu e3: Compa ison o p edic ed NOx wi h di e en
s a egies
IV. CONCLUSION
• NOx emissions a e mainly con olled by in-
cylinde empe a u e, oxygen concen a ion, and
mix u e hea capaci y.
• Wa e injec ion was he mos e ec i e me hod,
nea ly elimina ing NOx ac oss engine speeds
h ough cooling, hea abso p ion, and oxygen
dilu ion.
• EGR educed NOx by lowe ing oxygen a ailabili y
and inc easing mix u e hea capaci y, hough less
e ec i ely han wa e injec ion.
• Combus ion chambe dep h had a mode a e e ec ,
wi h shallowe chambe s lowe ing NOx due o
be e swi l and mixing.
• Highe engine speeds consis en ly educed NOx
because o sho e high- empe a u e esidence
imes.
• The bes esul s can be achie ed by combining
wa e injec ion wi h op imized chambe geome y
and mode a e EGR.
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