لخّصلي

cylinders either through direct mixing in the intake manifold
with air or through injection directly into the cylinder [13].The performance of a dual fuel engine
at idling and low loads can be improved by optimizing some
engine operating and design parameters, such as engine speed,
load, pilot fuel quantity, injection timing, intake manifold condition and intake gaseous fuel compositions [27,28].Dual fuel operation has
advantages compared to diesel counterparts and spark ignition
(SI) engines, theoretically higher thermal efficiency resulted
from faster burning, less toxic emissions, high power density,
strong ignition sources providing more reliable [20].However, the dual fuel engine has some pitfalls such as the
poor utilization of the LPG fuel at low and intermediate loads
which results in poor engine performance (drop in engine efficiency), high HC, CO emissions and misfiring at higher gas
inducted levels.Engine performance, combustion and emissions characteristics are discussed
at different sections to get the clear scenario on the effects of
using liquefied petroleum gas (LPG) in diesel engine in dual
fuel mode.By converting diesel engines to run on LPG we can significantly
reduce the problem of diesel pollution while also improving
emissions of greenhouse gases [21,22].Such conversions are
however not a simple matter of changing the fuel, many
technical problems present particularly with availability of
specific fuel supply system, fuel injection control and engine
optimization to ensure that the engine performance is maintained and the exhaust emissions are minimized [23].This pilot diesel fuel, auto ignites first
and acts as a deliberate source of ignition for the combustion
of the gaseous fuel-air mixture.The pilot diesel fuel, which is
injected by the conventional diesel injection equipment normally, contributes only a small fraction of the engine power
output.In this
literature review, studies with wide range of diesel engine sizes
and different types investigated at different operation conditions are reviewed.Thus the combustion process in a dual fuel engine is
complex as it combines the features of SI and CI engines
[15-19].A
dual fuel engine is basically a modified diesel engine in which
a LPG fuel, called the primary fuel is inducted along with
air.The primary gaseous fuel is compressed with air, but does not
auto ignite due to its high self-ignition temperature.Due to this poor thermal efficiency high level of unburnt hydrocarbons in the exhaust is
found [24-26,100,102].Similarly, different percentages of LPG
were applied to optimize the engine output.A small
amount of diesel, usually called the pilot, is injected as in a
normal diesel engine near the end of compression of the primary fuel-air mixture.The dual fuel engines can also be reverted back to
straight diesel operation easily [14].Poor part load performance results from
incomplete combustion of LPG.This fuel is the main source of energy input to the engine.