The Effect of LPG Composition on Combustion and Performance in a DME-LPG Dual-fuel HCCI Engine 2010-01-0336
The effect of the composition of propane (C₃H₈) and butane
(C₄H₁₀) in liquefied petroleum gas (LPG) was investigated in a
dual-fuel HCCI engine fueled with di-methyl ether (DME) and LPG.
The composition of LPG affects DME-LPG dual fuel HCCI combustion
due to the difference in the physical properties of propane that
and butane such as octane number, auto-ignition temperature and
heat of vaporization.
DME was injected directly into the cylinder at various injection
timing from 160 to 350 crank angle degrees (CAD). LPG was injected
at the intake port with a fixed injection timing at 20 CAD.
It was found that power output was increased with propane ratio.
This gain in power output resulted from increased expansion work
due to the better anti-knock properties of propane. However, higher
propane ratio made combustion efficiency decrease because of the
suppression in low temperature reaction of DME which determines
heat release amount of high temperature reaction.
Carbon monoxide (CO) emission was reduced and nitrogen oxide
(NOx) emission increased as the propane ratio increased. This was
because increased in-cylinder pressure and temperature, caused by
the prolonged ignition delay, induced oxidation of CO and formation
of NOx. However, due to the chain termination steps that occurred
with the addition of LPG, hydrocarbon (HC) emission was increased
as the propane ratio increased even though the in-cylinder
temperature was increased as well.
Given these findings pure propane may be the best fuel
composition for a DME-LPG HCCI engine when considering engine
performance. However, it should be noted that the use of pure
propane is accompanied by slight increases in HC and NOx