This document summarizes an experimental study on reducing oxides of nitrogen (NOx) emissions in a single cylinder diesel engine converted to run in dual fuel mode with compressed natural gas (CNG). Experiments were conducted with varying CNG substitution levels, exhaust gas recirculation (EGR) rates, and fuel injection pressures. The results show that NOx emissions increased with higher CNG substitution levels but decreased with higher EGR rates and injection pressures. Increasing injection pressure was more effective at reducing NOx emissions while maintaining brake thermal efficiency compared to increasing EGR. The study aims to determine effective ways to control NOx emissions from a diesel engine operating in dual fuel mode with CNG.

1. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print),
ISSN 0976 – 6499(Online) Volume 5, Issue 5, May (2014), pp. 66-74 © IAEME
66
REDUCTION OF OXIDES OF NITROGEN EMISSIONS IN SINGLE
CYLINDER DUAL FUEL ENGINE USING EXHAUST GAS
RECIRCULATION AND VARYING PRESSURES
B. Nageswara Rao1*
, Dr. B. Sudheer Prem Kumar2
, Dr. K. Vijaya Kumar Reddy2*
1*
School of Mechanical Engineering,
Vignan’s University, Vadlamudi, Guntur-522213, A.P, India
2, 2*
Department of Mechanical Engineering,
College of Engineering, JNT University, Hyderabad-500085, A.P
ABSTRACT
This is a well-known fact that the oxides of nitrogen emitted as exhaust from an internal
combustion engines effect negatively on environment and human health. A single-cylinder diesel
engine has been converted into a dual-fuel engine to operate with natural gas together with a pilot
injection of diesel fuel used to ignite the CNG–air charge. The CNG was inducted into the
combustion chamber via intake manifold. Injection pressures in dual fuel engines will play a vital
role in engine performance and emissions released. This paper focused on reduction of oxides of
nitrogen emissions of CNG inducted duel fuel diesel engine by introducing hot exhaust gas
recirculation and increasing fuel injection pressures. An experimental investigations were carried out
to find out the effect of injection pressure on performance and emissions of a diesel engine operated
with CNG inducted into the engine. Experiments have been conducted on a single cylinder, 4 stroke
compression ignition engine. Behavior of the engine at 10%, 20%, 30%, 40% and 50% substitution
of CNG with respect to Diesel was examined and compared them at different injection pressures at
various EGR substitutions.
Keywords: BMEP; CNG- Diesel Engine; EGR; Engine Performance; Exhaust Emissions.
INTERNATIONAL JOURNAL OF ADVANCED RESEARCH
IN ENGINEERING AND TECHNOLOGY (IJARET)
ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
Volume 5, Issue 5, May (2014), pp. 66-74
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2. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print),
ISSN 0976 – 6499(Online) Volume 5, Issue 5, May (2014), pp. 66-74 © IAEME
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I. INTRODUCTION
Compressed Natural Gas (CNG) has become a better option as a clean burning fuel of an IC
engine. In order to comply with the ever-stringent emission norms throughout the world and crunch
in petroleum reserves, the modern day automobile industry is compelled to hunt for new and
alternative means of fuel sources to keep the wheels spinning universally [1]. Paradoxical objectives
of attaining simultaneous reduction in emission along with high performance has provided with a
few alternative. Natural gas produces practically no particulates since it contains few dissolved
impurities (e.g. sulphur compounds). Moreover, natural gas can be used in compression ignition
engines (dual fuel diesel– natural gas engines) since the auto-ignition temperature of the gaseous fuel
is higher compared to the one of conventional liquid diesel fuel [3]. Dual fuel diesel–natural gas
engines feature essentially a homogeneous natural gas–air mixture compressed rapidly below its
auto-ignition conditions and ignited by the injection of an amount of liquid diesel fuel around top
dead center position. Natural gas is fumigated into the intake air and premixed with it during the
induction stroke. At constant engine speed, the fumigated gaseous fuel replaces an equal amount of
the inducted combustion air since the total amount of the inducted mixture has to be kept constant.
Furthermore, under fumigated dual fuel operating mode, the desired engine power output (i.e. brake
mean effective pressure) is controlled by changing the amounts of the fuels used. Thus, at a given
combination of engine speed and load, the change of the liquid fuel ‘‘supplementary ratio” leads to a
change of the inhaled combustion air, thus resulting to the alteration of the total relative air–fuel ratio
[1-3].
The fuel injection rate fuel nozzle design and fuel injection pressure all affect the
characteristics of the diesel fuel spray and its mixing with air in the combustion chamber [4-10]. The
increased injection pressure gave better results for brake specific fuel consumption and brake thermal
efficiency compared to the original and decreased injection pressures [11]. Injection pressures
decreased BSFC [12-14]. The peak cylinder pressure is reduced in the dual fuel operation mode
compared to the diesel single fuel operation mode. It has been reported that reductions in the
emissions of smoke and NOx can be achieved using DFC mode [6, 7]. By increasing fuel injection
pressure, pollution levels reduce due to complete combustion of fuel. Emissions are reduced at 200
bar with different manifold inclinations compared to other pressures. Finally, it is concluded that the
information obtained in this investigation is very much useful in reduction of pollution and
increasing the performance of the engine by varying the manifold inclination of the modern I.C
engines [15-19].
II. EXPERIMENTAL PROCEDURE
Series of several experimental cycles were conducted with varying CNG percentages and
iterations were done with varying exhaust gas recirculation and the results were compared. The
engine used in the present study is a Kirloskar AV-1, single cylinder direct injection, Water cooled
diesel engine with the specifications given in Table 1. Diesel injected with a nozzle hole of size
0.15mm.the engine is coupled to a dc dynamometer. Engine exhaust emission is measured. Load was
varied from 0.5 kilo watt to 3 kilo watts. The amount of exhaust gas sent to the inlet of the engine is
varied. At each cycle, the engine was operated at varying load and the efficiency of the engine has
been calculated simultaneously. The experiment is carried out by keeping the compression ratio
constant i.e., 16.09:1.

3. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print),
ISSN 0976 – 6499(Online) Volume 5, Issue 5, May (2014), pp. 66-74 © IAEME
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III. TABLE OF ENGINE SPECIFICATIONS
Table 1: specifications of engine
Fig.1: block diagram of experimental set up
Parts
AB-air box, m- measurement of air by manometer, Fw-fly wheel, ADM-alternator dynamometer,
i-fuel injector, C-computer for P-θ interface, V-valve for fuel control, EGA-exhaust gas analyzer,
S-piezo electric sensor for p-θ interfacing, PB- panel board, EP-exhaust gas probe, FT-fuel tank.
Type Four- stroke, single cylinder, Compression ignition engine with VCR
Make Kirloskar AV-1
Rated power 3.7 KW, 1500 RPM
Bore and stroke 80mm×110mm
Compression ratio 16.09:1, variable from 13.51 to 19.69
Cylinder capacity 553cc
Dynamometer Electrical-AC Alternator
Orifice diameter 20 mm
Fuel Diesel
Calorimeter Exhaust gas calorimeter
Cooling Water cooled engine
Starting Hand cranking and auto start also provided

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ISSN 0976 – 6499(Online) Volume 5, Issue 5, May (2014), pp. 66-74 © IAEME
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IV. RESULTS AND DISCUSSIONS
The formation of nitric oxide (NO) is favored by high oxygen concentration and high charge
temperature. NOx concentration is affected considerably by the presence of gaseous fuel–air mixture.
The concentration of NOx under dual-fuel operation is lower compared to the one under normal
diesel operation at the same engine operating conditions (i.e. engine speed and load) at all CNG flow
rates. The oxides of nitrogen measured during the experiment were plotted against various input
parameters.
Graph 1: NOx VS BMEP at various CNG substitutions
Graph 1 shows the increase in the NOx emissions with increase in CNG induction
proportions. For further cycles of experiment EGR was introduced along with the incoming air at
BMEPs above 30bar.
Graph 2: NOX Vs CNG% at different BMEPs
0
100
200
300
400
500
600
700
800
900
-5 5 15 25 35 45 55
NOX
BMEP
NOx VS BMEP at varoius CNG substitutions
diesel
10%CNG
20%CNG
30%CNG
40%CNG
50%CNG
0
100
200
300
400
500
600
700
800
900
0 10 20 30 40 50 60
NOx
CNG%
NOX Vs CNG% at different BMEPs
39.2 bar BMEP
46.5 bar BMEP
53.2bar BMEP

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It is clear from graph 2 that the NOx emissions increased with the CNG at all the BMEPs (or)
loads. There is 37% increase in the NOx from pure diesel to 50% CNG substitutions.
Graph 3: NOx Vs CNG % at various EGR substitutions
Exhaust Gas was recirculated through the incoming air at various proportions. From graph 3
it is observed that due to decrease in the oxygen in the inlet charge the formation of oxides of
nitrogen were decreased. There 29% all in the measured NOx with increase in exhaust gas
recirculation. But increase in EGR input decrease the brake thermal efficiency, this relation is seen in
graph 7.
Graph 4: NOX Vs EGR% at different CNG proportions
0
100
200
300
400
500
600
700
800
900
0 10 20 30 40 50 60
NOx
CNG%
NOx Vs CNG % at various EGR substitutions
0% EGR
10% EGR
17% EGR
22% EGR
26% EGR
500
550
600
650
700
750
800
850
0 5 10 15 20 25 30
NOx
EGR%
NOX Vs EGR% at different CNG proportions
diesel
10%CNG
20%CNG
30%CNG
40%CNG
50%CNG

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ISSN 0976 – 6499(Online) Volume 5, Issue 5, May (2014), pp. 66-74 © IAEME
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Graph 5 shows the variation of NOx with increase in the injection pressure at various CNG
substitutions. Increasing in the injection pressures has decreased the NOx emissions to the mode
value of 15% when compared to that of normal injection pressure.
Graph 5: variation on NOx with various Injection Pressures
Graph 6: Brake thermal efficiency Vs NOx for various injection pressures
Injection pressures increase decreased the NOx emissions as very less account of decrease or
loss of brake thermal efficiency.
400
450
500
550
600
650
700
750
800
850
0% CNG 10% CNG 20% CNG 30% CNG 40% CNG 50% CNG
NOX
variation on NOx with various Injection Pressures
200bar IP 225bar IP 250bar IP
5
10
15
20
25
30
35
600 650 700 750 800 850
BTE
NOx
Brake thermal efficiency Vs NOx for various
injection pressures
200bar IP
225bar IP
250bar IP

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Graph 7: Brake thermal efficiency Vs Nox at various EGR proportions
Graph 7 shows the cost of brake thermal efficiency at which the NOx was reduced by
increasing the exhaust gas recirculation. With increase in exhaust gas recirculation NOx decreased at
the cost of brake thermal efficiency. This makes increase in the injection pressure more feasible
when brake thermal efficiency is a constraint equally important to reduction of NOx.
V. CONCLUSION
The NOx emissions increased with increase in CNG induction proportions at all the BMEPs
(or) loads. There is 37% increase in the NOx from pure diesel to 50% CNG substitutions. For further
cycles of experiment EGR was introduced along with the incoming air at BMEPs above 30bar.There
29% all in the measured NOx with increase in exhaust gas recirculation. But increase in EGR input
decrease the brake thermal efficiency. Increasing in the injection pressures has decreased the NOx
emissions to the mode value of 15% when compared to that of normal injection pressure. Injection
pressures increase decreased the NOx emissions as very less account of decrease or loss of brake
thermal efficiency. This makes increase in the injection pressure more feasible when brake thermal
efficiency is a constraint equally important to reduction of NOx.
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