Diesel Engine Emissions and Performance Characteristics under Cape Chestnut Biofuel

doi:10.4236/jpee.2013.16002

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Journal of Power and Energy Engineering, 2013, 1, 9-14

Published Online November 2013 (http://www.scirp.org/journal/jpee)

http://dx.doi.org/10.4236/jpee.2013.16002

Open Access JPEE

Diesel Engine Emissions and Performance Characteristics

under Cape Chestnut Biofuel

Jedidah W. Maina1*, Ayub N. Gitau1, James A. Nyang’aya2

1Department of Environmental and Biosystems Engineering, University of Nairobi, Nairobi, Kenya; 2Department of Mechanical and

Manufacturing En g i n e ering, University of Nairobi, Nairobi, Kenya.

Email: *[email protected]

Received October 9th, 2013; revised November 11th, 2013; accepted November 19th, 2013

cense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

Cape Chestnut oil was processed to biodiesel thro ugh transest erification. Cape Chestnut kennels are reported to have oil

content of 60% - 63% [1]. Properties of biodiesel were determined and compared with those of diesel and engine tests

done at a constant speed of 1500 RPM on the biodiesel blends to evaluate their performance and emissions characteris-

tics. Performance evaluation was in terms of Brake Specific Fuel Consumption (BSFC), Brake Horse Power (BHP) and

Brake Thermal Efficiency (ETE). The eng ine was initially run on diesel to establish the reference characteristics before

running on biodiesel blends. The biodiesel was blended with diesel volumetrically to 80% (B80), 50% ( B50), 20% (B20)

and 5% (B5) the percentage being the volume of biodiesel in the blended fuel. Diesel fuel had the lowest BSFC fol-

lowed by B5 whose BSFC was 7.3% higher than that of diesel. BTE for B100 was lower than that of diesel by 20.3%

while that of B5 was 7.6% lower. Concentration of SO2 in B100 was 92.7% lower than that of diesel fuel while that of

B20 was 24.7% lower. NO and NO2 concentrations for B100 were around 15% higher than that of diesel. Particulate

matter of less than 10 µm diameter (PM10) for diesel was found to be 72% of the total collected fro m all the test fuels

as compared to that of biodiesel blends at 28%. The study concluded that Cape Chestnut biodiesel blends containing up

to 20% biodiesel can be used in an unmodified diesel engine since their performance and emission characteristics were

very similar to that of diesel but with reduced toxic gas emissions therefore friendly to the environment.

Keywords: Biodiesel; Transesterification; Performance; Emissions; Brake Specific Fuel Consumption; Brake Horse

Power; Engine Thermal Efficiency

1. Introduction

Biofuels are broadly defined as liquids, solids or gaseous

fuels that are predominantly or exclusive ly produced f rom

biomass. The main types of biofuels include ethanol,

biodiesel and biogas derived from crops residues or

wastes. All of these can be used as substitutes or supple-

ments for the traditional fossil fuels used for transporta-

tion, dom estic and industrial uses [2]. It has been the focus

of considerable amount of recent research because it is

renewable and reduces the emissions of some pollutants

[3]. Before recommending any alternative biofuel to be

used in existing technologies on a large scale, the envi-

ronmental compatibility factor has to be considered as

compared to conventional fuel [4].

Increased industrialization and urbanization of the

world have led to a steep rise in demand of petroleum

based fuels. Fossils fuels which constitute 80% of primary

energy consumed in the world are the primary contribu-

tors to Greenhouse Gas Emissions (GHG). Biofuels are

considered environmentally friendly in that they are re-

newable, biodegradable, natural lubricants and generate

acceptable quality of exhaust gases. Recently because of

the increase in crude oil prices, limited resources of fossil

oil and environmental concerns, there has bee n a renewed

focus in vegetable oils and animal fats to make biodiesel

[4].

Kenya spent more than Kshs 230 mil li on to import fuel

and other lubricants in 2010 [5]. The annual avera ge price

of oil in creased from US $79.16 per b arrel in 2010 to US

$110.6 per barrel in 2011 and the demand of petroleum

products gre w by 1.9 pe r cent from 3867.1 thousan d tones

in 2010 to 3941.6 thousan d tones in 2011 [6]. Household

*Corresponding a uthor.

Diesel Engine Emissions and Performance Characteristics under Cape Chestnut Biofuel

cooking is another important application where biofuels

can replace charcoal and firewood. Indoor air pollution is

reduced as clean burning fuels and vegetable oils replace

traditional biomass which contributes to respiratory ill-

ness [7].

Since 1990, research into the manufacture and use of

biofuels has grown. It has been reported that carbonyl

compound emissions for diesel powered vehicles have

exceeded those from conventional gasoline vehicles [8].

The depletion of easily accessible supplies of oil and the

high cost of extracting oils from deep seas, remote areas

and politically unstable regions have contributed to re-

newed interest in biofuels as an alternative and renewable

supply of transport fuels and to policies in many countries

that encourage production and mandate consumption of

biofuels. Concerns over global climate change have also

contributed to the renewed interest in biofuels such as the

desire for increased energy security and to support the

rural sector. The rapid increase in global demand for bio-

fuels over the next decad e or more will provid e opportu-

nities for Africa exporters because neither EU nor US is

expected to meet its consumption mandates completely

from domestic production [7].

In Kenya today, the commercial energy sector is domi-

nated by petroleum and electricity as the prime movers of

modern sector of the economy while wood fuel provides

energy needs of the traditional sector including rural

communities and the urban poor. At the national level

wood fuel and othe r biomas s account for about 68% of the

total primary energy consumption followed by petroleum

at 22%, electricity at 9% and others less than 1% [9]. The

Government has enacted a policy paper [9] and Legisla-

tion [10] that favors the development of bioethanol and

biodiesel. Therefore there is need to develop biodiesel

locally which can be produced most efficiently and ef-

fectively consi dering the land use, environm ent, economic

and social issues.

2. Materials and Methods

The engine tests were carried out on a Nissan TD27 die-

sel engine model.

2.1. Test Engine

The engine used was a turbo charged water cooled Nis-

san TD27 4 Cylinder with rated maximum power of 62

Kw/4300rpm. The engine was set to run at a constant

speed of 1500 rpm. The test engine was coupled to a hy-

draulic G-type Froude dynamometer. The loads were

applied by regulating the amount of water going into the

dynamometer, with load increments in steps of 0.225 Kg.

The engine was connected to a pipette to measure fuel

consumption as shown in Figure 1. The 150 ml pipette

was to determine the fuel consumption. The fuel to the

Figure 1. Test diesel engine assembly.

engine was supplied from special hoppers/containers

arranged as shown in Figure 1. Each of the containers

was filled with a different fuel blend. With diesel, B100,

B80, B50, B20 and B5 in the respective containers la-

beled 1, 2, 3, 4, 5 and 6. Individual gate valves on the

fuel lines facilitated the changing to any of the fuel

blends for engine testing.

2.2. Fuel System

The fuel system consisted of fuel hoppers, deliv ery lines,

fuel filters, and injector pumps injector nozzles and over

flow lines. From the fuel hoppers, fuel flows by gravity

through the delivery lines to the filters to the injector

pumps.

2.3. Cooling System

The engine set up was water-cooled, with water flow

assisted by the engine’s water pump. The external circuit

was via a header tank, fitted with a thermometer. The

water temperature in the header tank was maintained at

120˚F (49˚C) by supplying cold water from the mains

and allowing the same amount of hot water to pass to

waste from the system. Thermometers were fitted to

measure the inlet and outlet water temperatures at the

engine.

2.4. Portable Toxic Gas Monitor

These are instruments used to detect and analyze toxic

vapours from the exhaust gases of the test engine. The

instruments were portable, light and easy to use. Each

digital measurements of a particular exhaust gas emission

in low concentrations were viewed in real time from the

monitors. The emission gases which were detected and

Open Access JPEE

Diesel Engine Emissions and Performance Characteristics under Cape Chestnut Biofuel 11

monitored were; SO2, NO and NO2. In order to detect

and measure the particulate matter (PM10) filters were

attached to the engine exhaust pipe. The readings from

the monitors were analyzed in real time of the engine.

2.5. Transesterification

The oil was transesterified using methanol as alcohol and

Potassium Hydroxide (KOH) as the catalyst. Every liter of

Cape Chestnut oil required 200 ml of methanol and the

amount of Potassium H y d ro xide was 1 % by weight of the

Methanol used. The catalyst was kept dry in an airtight

container during the storage since water promotes

saponification. The required amount of catalyst was

measured and dissol ved in t he alcohol befor e pouri ng int o

the corresponding volume of the Cape Chestnut oil. The

mixture was stirred and covered to avoid evaporation of

the alcohol into the atmosphere and left to settle for 24 hrs

after whic h there was a cle ar distin ction of b iodiese l at the

top and glycerin which settled at th e bottom. The alcohol

(methanol) reacted with the fatty acids in the Cape

Chestnut oil in the presence of the catalyst (Potassium

Hydroxide) to form mono alkyl (biodiesel) and glycerin.

2.6. Separation and Washing of the Biodiesel

After transesterification and overnight settling, results

showed methyl esters and glycerin distinctively sep arate.

Glycerin is denser and therefore settled at the bottom of

the containe r. The m ixture needed t o be se parated an d this

was done by sucking out the biodiesel from the top of the

container and leaving glycerin at the bottom to be dis-

posed of.

2.7. Biodiesel Drying

After gently washing three times with warm water, the

biodiesel was left overnight in the open for the evapora-

tion to take p lace and by the following day, all the water

had evaporated and biodiesel was ready for blending and

testing.

The process of biodiesel production from transesteri-

fication, separation, washing and drying took three days to

complete where upon blending was done by measuring

the necessary volumes of biodiesel. The volumes of bio-

diesel were 5, 20, 50 and 80 per cent while the balance of

the volume to make 100 per cent was diesel to make B5,

B20, B50 and B80 blends respectively.

2.8. Biodiesel Fuel Properties

2.8.1. Calorific Value

This was done with the help of a bomb calorimeter.

CTTWE in kj

HCV Mass ofFuel



 (1)

where HCV = Higher Cal orific Value; TWE = Total wate r

equivalence in calories; CT=Corrected temperature.

A graph was drawn to determine the corrected tem-

perature rise and then the Equation (1) employed.

Total water equivalent = volume of water in calorimeter

+ water equivalent of bomb.

2.8.2. Specifi c Gra vi t y

The specific gravity of fuel is necessary to determine the

power input of the fuel and hence determine the thermal

efficiency and BSFC. Thermal efficiency, brake horse

power and BSFC were the parameters used to determine

the performance of the fuels in the study. The val ue of 908

Kg/m3 [1] for the density of Cape Chestnut Methyl Ester

was used.

The specific gravity of the blends was calculated using

Equation (2) [11 ].

blend

SG SGii





 (2)

where SGblend is the specific gravity of blend and SGi

the specific gravity of component fuels and Xi is the

volume fraction of the mass i.

2.9. Fuel Consumption Measurement

The various fuels were used i n turns to run t he engine. The

time taken by test engine to consume 150 ml of each fuel

as indicated by the pipette was recorded. In order to start

the process th e p ipette was filled with fu el well abov e th e

top marking by opening the main supply valve. The en-

gine was operated on the main supply while isolating the

fuel from the pipet te. The m ain supply valve was t hen clo-

sed and the e ngine ope rated o n the fuel from the pi pette t o

determine the consumpti on. Subsequentl y , t he load was in-

creased by intervals of 0.225 Kg until the engine started to

run with difficulty at which point the load was considered

to be the maximum for that particular fuel at that speed.

2.10. Measurement of Exhaust Gases

The fuel consumption was recorded concurrently with

sampling of the emissions by the monitors attached to the

engine’s exhaust pipe. The emissions monitors were re-

cording the detected toxic gases NO, SO2 and NO2 at

intervals of every ten seconds in parts per million (ppm).

To evaluate the particulate matter emitted by fuels, a

filter was attached to the engine exhaust pipe which en-

abled it to pick any PM10 emitted as the exhaust gases

exited. Two filters were used, for the diesel and the other

for B100, B80, B50, B20 and B5. The reason why only

one filter was used for all the CCME and its blends is

because the PM10 in them was almost negligible for each

to be considered independently.

2.11. Evaluation of Exhaust Emission Gases and

Particulate Matter

The evaluati ons were d one for t he exhaust e missions f rom

Open Access JPEE

Diesel Engine Emissions and Performance Characteristics under Cape Chestnut Biofuel

each fuel running the diesel engine and their quantities in

ppm compared to that of dies el . The em i ssion gase s und e r

consideration were NO, SO2 and NO2. Particulate matter

was also analyzed for neat CCME and its blends and a

comparison was also done with No 2 diesel. To illustrate

the comparison, graph s were drawn to show the tr ends of

each emission gas with time as the engine load was in-

creased which was analyzed as real time. Comparisons

were also done on the fuels to determine the trend on

increasing the percentage of biodiesel in blend with con-

ventional diesel.

2.12. Determination of Brake Power

The loading of the engine was done through the dyna-

mometer which in this study was hydraulic. Brake power

which is the engine power output was calculated from the

load to the engine through dynamometer, dynamometer

shaft speed which in our case was constant at 1500 rpm.

As specified earlier the dynamometer used was Froude

Type-G hydraulic dynamometer. The manufacturer rec-

ommended the Equation (3) below to determine the en-

gine brake power.

0.7457

BrakePower200

WN

 (3)

where W = Weight in pounds;

N = Dynamometer shaft speed in RPM;

0.7457 and 200 are constants.

2.13. Determination of Brake Specific Fuel

Consumption (BSFC)

This is calculated from the engine brake power, time (t)

taken to consume the fuel, density and volume of the fuel

because it is the mass flow rate of fuel consumed per unit

power output. It is expressed in Kg/Kw as shown in

Equation (4).



Density Volume 3600

BSFCKgKw h

Brake Powert











(4)

where: t = time taken in seconds to consume a particular

volume of fuel.

2.14. Determination of Thermal Efficiency

This is engine brake power output as a percentage of the

brake power inpu t of the fuel. Therefore to determine the

thermal efficiency, power input had to be determined first

and Equation (5) employed.



DensityVolumeheating value

Powe InputKw







(5)

where: t is the time taken to consume a particular volume

of fuel.

After evaluating the power input it was then possible to

determine the thermal efficiency as illustrated in Equation

(6).



BrakePower

Thermal Efficiency%

Powe Input

 (6)

3. Results and Discussion

3.1. Engine Performance

The engine performance tests carried out were to deter-

mine the BSFC, BHP and ther mal efficiencies of B5, B20,

B50, B80 and B100 Cape Chestnut biodiesel blends. The

results were compared to those of diesel under the same

conditions. Graphs were drawn of BSFC and thermal

efficiency each against BHP for all the biodiesel blends

and diesel.

3.1.1. Effect of Blending on Brake Specific Fuel

Consumption (BSFC)

Table 1 shows the results of the variation of BSFC with

brake power for the diesel, Cape Chestnut Methyl Ester

(CCME) and their various blen ds. The brake specific fuel

consumption (BSFC) in all the fuels tested decreased as

brake power (BP) increased up to and until BHP of 11 Kw

as shown in Figure 2.

3.1.2. Effect of Blending on Thermal Efficiency

Table 2 shows the results of thermal efficiencies while

Figure 3 shows the trend of thermal efficiency as plotted

against brake horse power for all the test fuels. At the

break power of 11 Kw the thermal efficiency difference

between diesel and B100 was found to be 8.99% which

was a decrease of 31%.

3.2. Analysis of Exhaust Gases from the Test

Engine

The tests were done to detect and determ ine the concentra-

tion of and types of gases in the exhaust emissions during

the running of the engine on Cape Chestnut biodiesel

blends and therefore compared with their concentration

during use of diesel fuel. The exhaust emission gases

R² = 0.972

R² = 0.913

R² = 0.994

R² = 0.899

R² = 0.764

R² = 0.921

0.25

0.30

0.35

0.40

0.45

0.50

579111315

BSFC (Kg/ KW h )

BHP (KW)

Diesel

B20

B50

B80

B100

Figure 2. BFSC Vs BHP.

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Diesel Engine Emissions and Performance Characteristics under Cape Chestnut Biofuel

Open Access JPEE

Table 1. Brake specific fuel consumption for test fuels.

BHP (Kw) Brake Specific Fuel Consumption (BSFC), Kg/Kw·h

Diesel B5 B20 B50 B80 B100

5.593 0.444 0.446 0.457 0.457 0.475 0.488

8.389 0.323 0.334 0.364 0.384 0.397 0.449

11.186 0.28 0.340 0.348 0.399 0.430 0.426

13.982 0.318 0.343 0.381 0.405 0.490 0.483

Table 2. Thermal efficiency of the test fuels.

BHP (Kw) Brake Thermal Efficiency, %

Diesel B5 B20 B50 B80 B100

5.593 18.258 18.143 18.069 18.798 18.093 18.948

8.389 24.852 24.222 22.644 22.412 21.669 20.603

11.186 28.706 23.771 23.693 21.573 20.001 21.715

13.982 25.256 23.607 21.684 20.319 18.500 19.13

R² = 0.978

R² = 0.999

R² = 0.996

R² = 0.965

R² = 0.967

R² = 0.882

579 11131517

SO2 (ppm)

B.H.P (kW )

Diesel

B20

B50

B80

B100

Figure 4. The variation of SO2 with BHP for test fuels.

Figure 3. Thermal efficiency Vs BHP.

in the study were the SO2, NO2, and NO.

3.2.1. Analysis of SO2 Emissions from the Test Fuels

The exhaust gases from the test fuels were analysed and

the results of S02 concentration are as shown in Table 3.

As brake power increased, the SO2 emissions in the fuels

increased reaching a peak at about 11 Kw as shown on

Figure 4. The SO2 at 11 Kw for B100 wa s 2.16 1 ppm and

19.917 ppm for No. 2 diesel an reduction of 17.756 ppm

which is 89% reduction in emissions.

3.2.2. Anal ysi s of NO Emissions fr om the T e st Fuels

As shown i n th e grap hs i n Figure 5, as brake horse power

was increased, NO emissions concentrations showed a

linear increa ment. B100 was found to have the highest NO

emissions of 2.042 ppm as compared to diesel with 1.874

ppm at BHP of 13.98 Kw.

Figure 5. The variation of NO with BHP for test fuels.

with the increase of BHP up to around BHP of 11 Kw and

were found to rise as BHP increased. The NO2 emissions

detected in diesel at BP of about 11 Kw was 0.442 ppm

while B1 00 was 0.5 29 ppm a devi ation of 0 .087 ppm from

hat of diesel and an increase of 19.7%.

3.2.3. NO2 Emissions from the Test Fuels t

NO2 emissions for all the test fuels were found to decrease

Diesel Engine Emissions and Performance Characteristics under Cape Chestnut Biofuel

Table 3. SO2 emissions for test fuels.

BHP (Kw) SO2 (ppm)

Diesel B5 B20 B50 B80 B100

5.593 3.524 3.033 2.963 2.2672.467 0.000

8.389 15.789 13.167 11.173 10.8923.533 1.233

11.186 19.917 15.300 12.400 9.2293.050 2.161

13.982 7.258 10.447 8.458 3.4181.967 0.000

3.2.4. Concent ration of Particulate Matter (PM) in

the Test Fuels

Particulate matter detected while carrying out the tests

were of two types, fine and course particles. diesel fuel

had 78% of the total percentage of fine particles detected

while biodiesel blends combined had 22%.

4. Conclusions

The study analysis concluded that:

 The use of biodiesel leads to reduced engine power as

observed in the high BSFC as the volumetric per-

centage of biodiesel increased in the blends. The use of

biodiesel in small amounts in the blends with diesel

resulted in insignificant power loss.

 The main reason for power loss is attribut ed to reduce d

heating value of the biodiesel as compared to diesel

fuel because of its high density therefore m ore volum e

of biodiesel is needed to produce equivalent power

output as compared to diesel.

Where modification to an engine is done the injection

feature of biodiesel is influential to engine power con-

sidering biodiesel has a higher density and viscosity.

5. Acknowledgements

My sincere thanks to the Departments of Environmental

and Biosystems Engineering and Mechanical and Manu-

facturing Engineering of the University of Nairobi for

providing support in the course of the research of this

work.

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