06-08-2013, 03:52 PM
Performance, emission and combustion characteristics of a DI diesel engine using waste plastic oil
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ABSTRACT
Increase in energy demand, stringent emission norms and depletion of oil resources have led the
researchers to find alternative fuels for internal combustion engines. On the other hand waste plastic
pose a very serious environment challenge because of their disposal problems all over the world. Plastics
have now become indispensable materials in the modern world and application in the industrial field is
continually increasing. In this context, waste plastic solid is currently receiving renewed interest. The
properties of the oil derived from waste plastics were analyzed and compared with the petroleum prod-
ucts and found that it has properties similar to that of diesel. In the present work, waste plastic oil was
used as an alternate fuel in a DI diesel engine without any modification. The present investigation was to
study the performance, emission and combustion characteristics of a single cylinder, four-stroke, air-
cooled DI diesel engine run with waste plastic oil. The experimental results have showed a stable perfor-
mance with brake thermal efficiency similar to that of diesel. Carbon dioxide and unburned hydrocarbon
were marginally higher than that of the diesel baseline.
Introduction
Plastics have become an indispensable part in today’s world.
Due to their lightweight, durability, energy efficiency, coupled with
a faster rate of production and design flexibility, these plastics are
employed in entire gamut of industrial and domestic areas. Plastics
are produced from petroleum derivates and are composed primar-
ily of hydrocarbons but also contain additives such as antioxidants,
colorants and other stabilizers [1,2]. Disposal of the waste plastics
poses a great hazard to the environment and effective method has
not yet been implemented.
Waste plastic oil in diesel engines
Diesel engines are most preferred power plants due to their
excellent driveability and higher thermal efficiency. Despite their
advantages, they emit high levels of NOx and smoke which will
have an effect on human health. Hence, stringent emission norms
and the depletion of petroleum fuels have necessitated the search
for alternate fuels for diesel engines. On the other hand, due to the
rapid growth of automotive vehicles in transportation sector, the
consumption of oil keeps increasing. Most of the research work
has been done by mixing oil developed from waste plastic disposal
with heavy oil for marine application .The results showed that
waste plastic disposal oil when mixed with heavy oils reduces
the viscosity significantly and improves the engine performance.
However, very little has been done to test their use in high-speed
diesel engines.
Conversion process
The feed system consists of equipments for sizing hard, thick
flexible and thin flexible materials, which normally constitutes
the municipal waste stream. The system essentially consists of
sorters and sizing equipments like crusher, cutter and shredder.
The various sizes and shapes of the material are sorted into catego-
ries suitable for crushing, cutting and shredding. The sorted mate-
rial was crushed or cut or shredded and graded into uniform size
for ease of handling and melting in the melting/preheating process.
This process of sizing and grading the waste was semi automatic.
The graded feed was stored in a hopper before feeding to the pro-
cess by a conveyor feeder. The sorted feedstock of known compo-
sition was stored separately for proportionate feeding for
processing nonstandard feed design or processing special feed de-
signs. The dust and other fine wastes collected from the cyclone fil-
ter were disposed through a vent with particle size monitoring
system. The assorted waste plastic was fed into a reactor along
with 1% (by weight) catalyst and 10% (by weight) coal and main-
tained at a temperature of 300 °C to 400 °C at atmospheric pres-
sure for about 3 hours to 4 hours.
Cylinder pressure crank angle diagram
Fig. 3 indicates the cylinder pressure with crank angle for both
fuels at rated power. The cylinder peak pressure for diesel is 67 bar
at rated power and 71 bar in the case of waste plastic oil. Higher
cylinder pressure in the case of waste plastic oil compared to diesel
is due to the evaporation of waste plastic oil inside the cylinder by
absorbing heat from the combustion chamber. Longer ignition de-
lay at high load range increases the pressure of waste plastic oil
than that of diesel. In other words, this period depicts the abnormal
combustion or premixed combustion. However, this is the usual
behaviour of high-octane fuel in high compression ratio engines.
This can be controlled by proper selection of compression ratio.
Carbon monoxide
The variation of carbon monoxide with brake power is shown in
Fig. 8. Generally, CI engine operates with lean mixtures and hence
the CO emission would be low. CO emission is toxic and must be
controlled. It is an intermediate product in the combustion of a
hydrocarbon fuel, so its emission results from incomplete combus-
tion. Emission of CO is therefore greatly dependent on the air fuel
ratio relative to the stoichiometric proportions. Rich combustion
invariably produces CO, and emissions increase nearly linearly
with the deviation from the stoichiometry [13]. The concentration
of CO emission varies from 14.14 g/kWh at 25% of rated power to
5.75 g/kWh at rated power for diesel, whereas it varies from
18.51 g/kWh at 25% of rated power to 6.19 g/kWh at rated power
for waste plastic oil. The results show that CO emission of waste
plastic oil is higher than diesel. The reason behind increased CO
emission is incomplete combustion due to reduced in-cylinder
temperatures. The drastic increase in CO emission at higher loads
is due to higher fuel consumption.
Conclusion
From the tests conducted with waste plastic oil and diesel on a
DI diesel engine, the following conclusions are arrived:
Engine was able to run with 100% waste plastic oil.
Ignition delay was longer by about 2.5 °CA in the case of waste
plastic oil compared to diesel.
NOx is higher by about 25% for waste plastic oil operation than
that of diesel operation.
CO emission increased by 5% in waste plastic oil compared to
diesel operation.
Unburned hydrocarbon emission is higher by about 15%.
Smoke reduced by 40% at rated power in waste plastic oil com-
pared to diesel operation.
Engine fueled with waste plastic oil exhibits higher thermal effi-
ciency upto 75% of the rated power.