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© Adama Science & Technology University https://ejssd.astu.edu.et

Ethiopian Journal of Science and Sustainable Development (EJSSD)

p-ISSN 1998-0531 Volume 5 (2), 2018

Experimental investigation on effect of injection timing in

multiple injection on NOx and smoke from CRDI diesel engine

fuelled with biodiesel blend

Ramesh Babu Nallamothu1,*, Anantha Kamal Nallamothu2, Seshu Kishan

Nallamothu3, IN Niranjan Kumar4, BV Appa Rao4

1
Mechanical Systems and Vehicle Engineering Department, Adama Science and

Technology University, P.o. Box: 1888, Adama, Ethiopia
2
Vellore Institute of Technology, Vellore, India.

3
SRM Institute of Science and Technology, Chennai, India

4
Marine Engineering Department, Andhra University, Visakhapatnam, India.

*corresponding author, e-mail: rbnallamothu@gmail.com, Mobile: +251 912234395

Abstract

Diesel engines with their high thermal efficiency and fuel economy are very much

successful in commercial applications compared to their counterpart gasoline engines.

The emissions like HC and CO from diesel engines are less compared to gasoline

engines because they run mostly with lean mixtures. But due to heterogeneous

combustion NOx and smoke emissions from Diesel engines is high. Due to contradicting

requirements for the reduction of NOx and smoke, the tradeoff between NOx and smoke

emission without compromising fuel economy is a big challenge being faced by

automotive industries and researchers in the field. Biodiesel produced from non-edible

feed stock is found to be a good alternative to petro diesel. Cotton seed oil biodiesel is

produced using transesterification process and characterized for its properties. The

blend B20, which is most accepted and does not need any modifications of the engine,

is used as fuel. It is observed that the formation of NOx is very much dependent on the

peak temperature in the combustion chamber. Various types of techniques are being

tried by the researchers to reduce high NOx emission from usage of biodiesel blended

fuel in diesel engines. The techniques used are like dilution using EGR, injection of

water, retardation of injection timing etc. With the development of CRDI systems split

and multiple injection strategy attracting the attention of researchers as a promising

technique in reducing the NOx emissions. In this work an attempt is made to study the

effect of retardation of injection timing of a selected multiple injection with pilot-main-

post strategy. The selected strategy is with 10% pilot fuel quantity with a dwell of 10

CAD and closely coupled fixed quantity of 0.5 mg post injection with 3 CAD after main

injection. The main injection timing along with pilot and post was retarded from the

recommended 23° bTDC in steps of 3 degrees. It is observed that the combination of

multiple injection and retardation of injection reduced NOx emissions effectively

without compromising power output and thermal efficieny.

Keywords: Biodiesel blend, Emission, Pilot injection, Post injection,

Transesterification

mailto:rbnallamothu@gmail.com

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1. Introduction

Recently, the extinction issue of fossil

fuel due to continuous usage become the

focus attention for all of people in the

world who depend on this energy source

in every of their activity. The people

attention is also increasingly focused on

fossil fuel due to the fact that continuous

usage of this fuel believed causes

environmental problem i.e. air pollution

and global warming. Fossil fuels

reservoirs around the world are declining

due to their non-renewable nature. At the

same time the demand for energy is,

continuously, increasing to meet the

needs of the world population, which is

growing significantly. Global warming is

being caused by the greenhouse gas

emissions. Reducing the dependence on

fossil fuels will be beneficial, from

environmental point of view, since this

will reduce the concentration of carbon

dioxide in the atmosphere. Hence,

currently the world has been tried to look

for a solution by exploring and using an

alternative fuel which is renewable,

environmental friendly, sustainable

availability and economically feasible

sources of energy have emerged as a

priority for research to resolve all these

problems (Putrasar et al., 2013).

Therefore, explorations to find

Biodiesel are one of the most promising

alternative fuels to replace or to reduce

dependency on the conventional

petroleum-based fuels with multiple

environmental advantages and application

in compression ignition (CI) engines

with no modification. Biodiesel is

nonexclusive, biodegradable, non

flammable, renewable, nontoxic,

environment friendly, and similar to

diesel fuel (Atabani et al., 2013).The

main advantages of biodiesel include the

following: it can be blended with diesel

fuel at any proportion; it can be used in a

CI engine with no modification; it does

not contain any harmful substances; and

it produces less harmful emissions to the

environment than diesel fuel. Biodiesel,

popularized as the mono alkyl esters are

derived from triglycerides (vegetable oils

or animal fats).Transesterification is the

most convenient process to convert

triglycerides to biodiesel.

Transesterification process involves a

reaction of the triglyceride feedstock

with light alcohol in the presence of a

catalyst to yield a mixture of mono alkyl

esters currently, using hydroxides of

sodium or potassium, is the common

route for industrial production of

biodiesel (Pushparaj et al., 2013).

The minimization of fuel

consumption and the reduction of

emissions have been two driving forces

for engine development throughout the

last decades. The first objective is in the

financial interest of the vehicle owners.

The second is imposed by legislation,

sometimes also supported by excise

reductions or customers’ demands for

clean engines.

The ongoing emission of NOx is a

serious persistent environmental problem

due to; it plays an important role in the

atmospheric ozone destruction and

global warming (Busca et al., 1998).

NOx is one of the most important

precursors to the photochemical smog.

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Component of smog irritate eyes and

throat, stir up asthmatic attacks, decrease

visibility and damages plants and

materials as well. By dissolving with

water vapor NOx form acid rain which

has direct and indirect effects both on

human and plants. An SCR (Selective

Catalytic Reduction) exhaust gas after

treatment system which uses urea

solution as a reducing agent has a high

NOx reduction potential and is a well-

known technique for stationary

applications (Bosch et al., 1988). The

idea of using urea SCR systems for the

reduction of NOx emissions in diesel

engines is two decades old. Since then,

many applications have been developed,

some of which have reached

commercialization (Perry et al., 2013).

But, it is still a challenge for researchers.

With the recent development of

common rail direct injection system, it

became possible to reduce NOx and other

emissions by adopting multiple injection

strategy (Imarisio et al., 2000; Badami et

al., 2002).

Split fuel injection involves reducing

splitting the injection as two or more

events which can lead to a reduction in

the ignition delay in the initial fuel pulse.

This leads greater fraction of combustion

to occur later in the expansion stroke. As

majority of NOx occurs during premixed

stage, the net amount of NOx formed

during the split fuel injection is lowered

(Gao et al., 2001). Multiple injections

method is found to be very effective at

reducing particulate emissions at high

load, and combined technique of multiple

injections with EGR is effective at

intermediate and light loads. However,

increased particulate emissions due to

EGR causes increased engine wear due to

degradation of lubricant. Increased Brake

Specific Fuel Consumption (BSFC) is

another concern. Split injection up to 5

splits, are experimented in combination

with EGR (Wang et al., 2007). The

injection timing of 35o bTDC leads to

insufficient combustion causing increase

in the level of HC. Fuel consumption

increases with early injection due to

insufficient combustion in the initial

combustion duration. Introduction of

pilot injection reduces the flame

temperature reducing the amount of NOx

emission. When the quantity of pilot

injection is increased the level of noise

reduces (Syed et al., 2015). Effects of

start of pilot injection, start of main

injection and fuel injection pressure on

engine performance, emissions and

combustion characteristics of Karanja

biodiesel blends compared to mineral

diesel were investigated at 1500 rpm in a

single cylinder CRDI engine. BSFC of

test fuels increased with increasing

concentration of Karanja biodiesel.

Lower Karanja biodiesel blends showed

lower brake specific CO and HC

emissions in comparison to mineral

diesel but BSHC emissions of KOME50

were higher than mineral diesel at some

operating conditions. Brake specific

NOx emissions from KOME20 and

KOME10 were higher than mineral

diesel. At different SOPI timings and

fixed SOMI timing, BSNOx emissions

were almost similar for all test fuels.

BSNOx emissions were higher for 1000

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bar FIP in comparison to 500 bar FIP.

Combustion duration of KOME50 was

higher than mineral diesel due to relatively

inferior mixing characteristics and

requirement of larger fuel quantity. This

experimental investigation shows that

utilization of 10% or 20% Karanja

biodiesel blends in CRDI engines with

pilot injection can be useful in improving

engine efficiency and reducing emissions

(AtulDhar et al., 2015).

For solving the problems like depletion

of fossil fuels and environmental

degradation, biodiesel usage in diesel

engines is widely investigated. The

performance of cotton seed oil biodiesel

is investigated on a single cylinder CIDI

engine at a constant speed of 1500 rpm

and field compression ratio 0f 17.5 at

different load conditions. The

performance, combustion and emission

parameters are measured and compared

with baseline results of diesel fuel. The

brake thermal efficiency of cotton seed

oil methyl ester (CSOME) was lower

than that of petro diesel and brake

specific fuel consumption was found to

be higher. However, biodiesel resulted in

the reduction of carbon dioxide, un-burnt

hydrocarbon, and smoke opacity at the

expense of nitrogen oxides. Carbon

monoxide emissions for biodiesel was

higher at maximum output power. It has

been found that the combustion

characteristics of cotton seed oil methyl

ester closely followed those of standard

petro diesel. The experimental results

suggested that biodiesel derived from

cotton seed oil could be used as a good

substitute to petro diesel fuel in a

conventional diesel without any

modification (Rao et al., 2014). In this

work B20 was used as fuel, since B20 is

mostly accepted and does not need in

modifications of the engine.

2. Methodology

This work is done with the main

objective of investigating the effect of

multiple injection strategy with varying

injection timing and dwell period on

harmful emissions from CRDI diesel

engine fueled with biodiesel blend.

Cotton seed oil is used for the preparation

of biodiesel. Biodiesel is prepared using

transesterification process.

A novel scheme of experiments is

adopted in the work to understand the

influence of multiple injections by

varying different parameters on the

emissions from the engine.

The used injection strategy is pilot

(pre)-main-post. The pilot is fixed at 10%

and post fuel quantity is fixed as

0.5mg/cycle.

The following were the steps

followed in this work:

• Extraction of oil from cotton seeds

using mechanical press

• Preparation of biodiesel using

tranesterification process

• Characterization of biodiesel

• Preparation of B20 blend

• Testing the performance of CRDI

diesel engine with B20 with multiple

injection strategy varying injection

timing

• Comparing the emissions from

multiple injection and single

injection.

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© Adama Science & Technology University https://ejssd.astu.edu.et

Engine setup

The setup consists of single cylinder,

four stroke, CRDI VCR (Variable

Compression Ratio) engine connected to

eddy current dynamometer. Specification of

the CRDI Engine is given in Table 1. It is

provided with necessary instruments for

combustion pressure, crank angle,

airflow, fuel flow, temperatures and load

measurements. These signals are

interfaced to computer through high

speed data acquisition device.

The setup has stand‐alone panel box

consisting of air box, twin fuel tank,

manometer, fuel measuring unit,

transmitters for air and fuel flow

measurements, process indicator and

piezo powering unit.

Rotameter are provided for engine

cooling water flow measurement. CRDI

VCR engine works with programmable

Open ECU for Diesel injection, fuel

injector, common rail with rail pressure

sensor and pressure regulating valve,

crank position sensor, fuel pump and

wiring harness.

The setup enables study of CRDI VCR

engine performance with programmable

ECU at different compression ratios and

with different EGR. Engine performance

study includes brake power, indicated

power, frictional power, BMEP, IMEP,

brake thermal efficiency, indicated

thermal efficiency, Mechanical

efficiency, volumetric efficiency,

specific fuel consumption, Air fuel ratio,

heat balance and combustion analysis.

NOx is measured using AVL Digas 444N

exhaust gas analyser and Smoke is

measured using AVL 437C Smoke

meter.

A novel scheme of experiments is

adopted in the work to understand the

influence of multiple injections by

varying different parameters on the

emissions from the engine. The injection

is split into pilot (pre)-main-post. After

different trials the quantity of Pilot

injection is fixed as 10% and post fuel

quantity is fixed as 0.5 mg/cycle. The

dwell between main and pilot is

maintained as 10 degrees. Closely

coupled post injection is used with 3

degrees after main injection. Main

injection timing is retarded from

recommended injection timing of 23o to

11o bTDC. The influence of this

retardation on NOx emission and smoke

is measured. B20P10M20P3 stands for

Biodiesel blend 20, pilot injection with

dwell of 10o, Main injection at 20o and

post injection with dwell of 3o.

Table 1. Specification of the CRDI Engine

Engine Kirloskar, single cylinder, four stroke water cooled, VCR

Stroke 110 mm

Bore 87.5 mm

Capacity 661 cc

Power 3.5 kW

Speed 1500 RPM

Compression Ratio 12-18

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© Adama Science & Technology University https://ejssd.astu.edu.et

100

200

300

400

500

600

700

800

900

D M23 B20 M23 B20 P10
M23 P3

B20 P10
M20 P3

B20 P10
M17 P3

B20 P10
M14 P3

B20 P10
M11 P3

N
O

x
P

P
M

3. Result and Discussion

The properties of prepared cotton

seed oil biodiesel is given in table 2. It is

observed from the chart (Figure 1 to 4)

that the NOx emission is greatly affected

by injection timing. At all loads the

selected injection strategy has influence

on the NOx emission. At part loads the

the effect is very much prominent.

As the injection timing is retarded the

NOx emission observed to be reducing

due to reduction in the peak temperatures

developed in the combustion chamber.

The reduction is about 45.93% with 75%

load at P10 M11 P3 compared to M23.

The reduction is 50.58% with 50% load

at P10 M11 P3 compared to M23.

Splitting the injection at M23 observed to

be not beneficial

Multiple injection strategy is

observed to be more effective in reducing

NOx at part load condition. There is an

increment in NOx with P10 M23 P3.

With B20 the engine was not running

smoothly with splitting the injection at

M23 and M20.

Table 2. Properties of biodiesel

Figure 1. NOx emission at 25% load

Properties B100

Density@15 oC, ( gm/cm3 ) 0.8865

Kinematics viscosity@40 oC 4.85

Flash point, oC 149

Fire Point, oC 160

Cloud point, oC +1

Gross Calorific Value, kJ/kg 40,695

Cetane number 50.8

Copper strip corrosion @ 50oC for 3 hrs Not worse than no 1

Acid value as mgof KOH/gm 0.063

Carbon Residue 0.041%

Sulphur 0.0043%

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200

400

600

800

1000

1200

1400

D M23 B20 M23 B20 P10
M23 P3

B20 P10
M20 P3

B20 P10
M17 P3

B20 P10
M14 P3

B20 P10
M11 P3

N
O

x
E

m
is

si
o

n
in

P
P

200

400

600

800

1000

1200

1400

D M23 B20 M23 B20 P10
M23 P3

B20 P10
M20 P3

B20 P10
M17 P3

B20 P10
M14 P3

B20 P10
M11 P3

N
O

x
E

m
is

si
o

n
in

P
P

200

400

600

800

1000

1200

1400

D M23 B20 M23 B20 P10
M23 P3

B20 P10
M20 P3

B20 P10
M17 P3

B20 P10
M14 P3

B20 P10
M11 P3

N
O

x
x

E
m

is
si

o
n

in
P

P
M

Figure 2. NOx emission at 50% load

Figure 3. NOx emission at 75% load

Figure 4. NOx emission at 100% load

Ramesh Babu et al. EJSSD, V 5 (2), 2018

0 5 10 15

S
m

o
k

e
%

Load %

D M23

B20 M23

B20 P10 M23 P3

B20 P10 M20 P3

B20 P10 M17 P3

B20 P10 M14 P3

B20 P10 M11 P3

It is observed that the retardation of

multiple injection with main injection

retardation from 23o bTDC to 11o bTDC,

smoke emission is considerably affected

(Figure 5). Smoke opacity reduced

gradually up to main injection 14o and

then starts increasing with further

retardation. The reduction is 69.1%,

62.23%, 58.93%, 48.68%, and 18.29%

with load of 0%, 25%, 50%, 75%, and

100% respectively at P10 M14 P3.

Reduction in smoke with multiple

injections is more at lower loads than

higher loads.

Figure 5. Smoke Emission with varying load

4. Conclusion

 Retardation of multiple injection up to

M11 helped in reducing both NOx

and smoke. Further retardation

caused increment in smoke.

 B20P10M14P3 observed to be better

for smoke. Smoke starts increasing

with further retardation.

 NOx observed to be reducing

continuously with retardation.

 P10 M11 P3 is better for smoke and

NOx tradeoff

 Multiple injection is a good means of

having tradeoff between smoke and

NOx emissions.

 It is a very complex process.

Numerous experiments are required

to have thorough understanding of

the influence of multiple injection.

 Dwell 10 is observed to be better

 Further combustion related analysis is

required to understand completely

the influence of multiple injection

 Multiple injection strategy seems to

be more efficient than conventional

in reducing emission due to their

capability in controlling heat release

rate and hence peak temperature.

 Multiple injection is better than single

injection in optimising tradeoff

between NOx and smoke due to their

efficiency in reducing initial high

temperatures and supporting

combustion of late injection.

Ramesh Babu et al. EJSSD, V 5 (2), 2018

 Reduction in emissions was improved

with multiple pre-main-post

injection strategy, as pre injection

supports main injection combustion

and reduced delay while post

combustion helped in oxidation of

soot particles without impact on

NOx.

 Proper dwell between injections was

significant as small dwell led to

situation of single injection while

long reduced the effect of pre-mix

combustion. For pilot injection dwell

around 10 CAD observed to be better

for reducing harmful emission

efficiently.

 Around 21 CAD bTDC injection

timing of first injection was observed

to be optimum for simultaneous

reduction of NOx and soot.

 Multiple injection strategy is more

effective in reducing smoke

emissions at lower loads.

 The rate of increase in smoke

emission is high as load increases

with multiple injection strategy.

Acknowledgment

We are thankful to Marine

engineering department, Andhra

University, for giving this opportunity to

work on biodiesel applications in diesel

engines. We are also thankful to Sri

Venkateswara research center,

Kanchipuram for providing necessary

research facilities.

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