Combustion and emission of rapeseed oil blends in diesel engine
L. Labecki, A. Cairns, J. Xia, A. Megaritis, H. Zhao, L.C. Ganippa
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Centre for Advanced Powertrain and Fuels Research (CAPF), School of Engineering and Design, Brunel University, Uxbridge, London UB8 3PH, UK
article info
Article history:
Received 6 October 2011
Received in revised form 9 February 2012
Accepted 13 February 2012
Available online 12 March 2012
Keywords:
Plant oil
Biofuel
Injection timing
Injection pressure
Diesel engine
Emissions
abstract
Combustion and emission characteristics of rapeseed plant oil (RSO) and its blends with diesel fuel have
been investigated in a multi-cylinder direct injection diesel engine. Plant oils have high viscosities com-
pared to diesel and this affects the performance and durability of automotive diesel engines when used
for longer time periods. Despite these adverse effects the exhaust emissions analysis show a significant
reduction in NO
x
and relatively higher amount of soot for RSO compared to diesel fuel. An attempt has
been made to reduce soot emissions from the combustion of RSO to exploit the advantage of its low
NO
x
emissions. The strategy of varying injection parameters such as injection pressures and injection tim-
ings have been used in this work to reduce the soot emissions for blends of 50% and 30% RSO in diesel
fuel. Using this strategy it was possible to achieve diesel equivalent levels of soot emission for 30%
RSO blend. Under diesel equivalent soot emission levels, it was also possible to achieve a further reduc-
tion in NO
x
emissions by up to 22% for 30% RSO blend, this was achieved at the expense of THC, CO and
BSFC. The exhaust soot particle number concentrations for 30% RSO blend reduces with an increase in
injection pressure and retarded injection timing. However, when compared to diesel, the exhaust soot
particle number concentration for 30% RSO blend was still higher, even after diesel equivalent level of
soot emission was achieved.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
Internal combustion engines that are fuelled by fossil fuels in
the automotive and power generation sectors are one of the main
sources of CO
2
and other hazardous pollutants. Fuels from renew-
able resources are beneficial from the environmental point of view.
The CO
2
produced from the combustion of biofuels can be effec-
tively absorbed by new growing plants during the process of pho-
tosynthesis, which in turn can be used to produce fuels; however
production process will also contribute to additional CO
2
produc-
tion. In the case of diesel engines several renewable fuels (mostly
biodiesel) are used to understand the effects of biodiesel on the en-
gine combustion and emission performance. However, in several
rural areas plant oils are used in diesel engines instead of biodiesel
for transportation, agriculture, small and large scale power gener-
ation, etc. Pure plant oils (PPO) are mainly produced form rape-
seed, soybean, jatropha, olive, palm, coconut, cottonseed, karanja,
sunflower, corn, and peanut [1]. For example, soya bean oil is dom-
inantly used in USA, rapeseed and sunflower oil in Europe, palm oil
in Southeast Asia, coconut oil in Philippines, jatropha and karanja
oil in India and the production of biodiesel from waste recycled
frying oil occurs in Japan [1,14]. These oils may be used for the
production of biodiesel (fatty acids methyl ester (FAME)) or
sometimes used as straight vegetable oils in diesel engines. PPO
contains triglycerides, where one molecule of glycerol is connected
to three molecules of long chain fatty acids. Approximately 60–70%
of fatty acids from PPO are mono-unsaturated and 10–20% are di-
unsaturated [1,2]. It has been reported that variation in content
and structure of fatty acids have a strong effect on combustion
and emission characteristics, depending upon both the degree of
saturation (amount of carbon double bonds) and the length of car-
bon chains present in PPO [3,4]. PPO also suffers from undesirable
properties such as lower calorific value, low Cetane number, high
viscosity (approximately 10–12 times lower than that of diesel)
which leads to problems associated with cold flow, cold start and
deposit formation in the injector, nozzle, combustion chamber,
and damaging rubber seals. All these problems make PPO as an
undesirable fuel for automotive applications as it affects the engine
durability when it is used continuously for a longer time period in
the engine. Despite these adverse effects there is an academic
interest in understanding the combustion and soot formation pro-
cesses of these fuels.
The problems related to higher viscosity of PPO can be ad-
dressed either through transesterification process or by blending
PPO with diesel or by preheating the fuel. The transesterification
process is a technique used to remove glycerol from PPO through
the addition of alcohol. The above described method leads to the
production of FAME which is more compatible with diesel engine
compared to PPO. Biodiesels can be used directly in diesel engines
0306-2619/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.apenergy.2012.02.026
⇑
Corresponding author.
E-mail address: lionel.ganippa@brunel.ac.uk (L.C. Ganippa).
Applied Energy 95 (2012) 139–146
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