13-08-2012, 02:32 PM
Simulation of compression engine powered by Biofuels
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Abstract
The present work describes a theoretical investigation concerning the performance of a four strokes compression
engine, which is powered by alternative fuels in the form of diesel–ethanol and diesel–ether
mixtures, the properties of which were sited from literature. The amount of each alcohol added was
5%, 10% and 15% by volume. The engine speed during the experimental work was within the range from
1000 to 4000 rpm, with engine was set at full throttle opening and hence the engine was operating under
full load conditions. Several parameters were calculated namely: engine torque, brake mean effective
pressure, brake power, specific fuel consumption and the thermal efficiency, this was carried out using
DIESEL-RK software.
It was found that the engine is of highest thermal efficiency when it is powered by a 15% ethanol–diesel
blend, wile it is of minimum thermal efficiency when it is powered by pure diesel fuel. Further, it was
found that both the thermal efficiency of the engine and the specific fuel consumption increases with
the percentage of either ethanol or ether in the fuel blend. However, the power was found to decrease
with the amount of either ethanol or ether in the fuel blends.
Introduction
It is well known that transport is almost totally dependent on
fossil, particularly, petroleum-based fuels such as gasoline, diesel
fuel, liquefied petroleum gas (LPG) and natural gas (NG). In the last
years, the world has been confronted with an energy crisis. The
most used fuel, petroleum, is becoming scarce and its use is associated
with the increase of environmental problems. Experts suggest
that current oil and gas reserves would suffice to last only a
few more decades. To exceed the rising energy demand and reducing
petroleum reserves, fuels such as biofuel are in the forefront of
the alternative technologies. Typical biofuels are biodiesel and
alcohol.
The importance of biodiesel has been pointed out in recent
works [1–7], and it is a very interesting alternative fuel to the diesel.
The biodiesel can be obtained from renewable sources, such as
vegetable oils or animal fats, through a transesterification process.
This comes from the fact that in order to use vegetable oil in a diesel
cycle engine without needing adaptations in the motor, it is
necessary to submit this oil to a chemical reaction denominated
transesterification, where the main objective is to reduce the oil
viscosity to a value close to that of the diesel.
Simulation model
The theoretical models used in the case of internal combustion
engines can be classified into two main groups viz., thermodynamic
models and fluid dynamic models. Thermodynamic models
are mainly based on the first law of thermodynamics and are used
to analyze the performance characteristics of engines. Pressure,
temperature and other required properties are evaluated with respect
to crank angle or in other words with respect to time. The engine
friction and heat transfer are taken into account using
empirical equations obtained from experiments. These models
are further classified into two groups namely single-zone models
and multi-zone models. On the other hand, multi-zone models
are also called computational fluid dynamics models. These are
also applied for the simulation of combustion process in the internal
combustion engines. They are based on the numerical calculation
of mass, momentum, energy and species conservation
equations in either one, two or three dimensions to follow the
propagation of flame or combustion front within the engine combustion
chamber.
Conclusions
In this work a four strokes compression engine was simulated
using a software. The simulation was performed in order to find
the performance of the engine when it is powered by different
types of fuels. The followings may be concluded from this study:
1. The addition of both ethanol and ether to diesel fuel will cause a
drop in the power output of the engine and hence the specific
fuel consumption will increase, while the thermal efficiency
will increase.
2. The addition of both ethanol and ether will have almost same
effect on the performance of the engine.