Abstract
A Liquefied Petroleum Gas (LPG)-diesel dual fuelled combustion experimental study was carried out to understand the impact of the properties of the direct injection diesel fuels, such as rapeseed methyl ester (RME) and gas-to-liquid (GTL), on combustion characteristics, engine performance and emissions. The experimental results showed that up to 60% of liquid fuel replacement by LPG was reached while keeping engine combustion variability within the acceptable range and obtaining clear benefits in the soot-NOx trade-off. However, the amount of LPG was limited by adverse effects in engine thermal efficiency, HC and CO emissions. LPG–RME showed a good alternative to LPG-diesel dual fuelling, as better engine combustion variability, HC, CO and soot behaviour was obtained when compared to the other liquid fuels, mainly due to its fuel oxygen content. On the other hand, NOx emissions were the highest, but these can be balanced by the application of EGR. LPG–GTL dual fuelling resulted in the highest NOx emissions benefit over a wide range of engine operating conditions. The high cetane number and the absence of aromatic of GTL are the main parameters for the more favourable soot-NOx trade-off compared to LPG–ULSD (ultra low sulphur diesel) dual fuelling.
Highlights
Liquefied petroleum gas (LPG) is considered as a promising alternative fuel and has been widely used in transportation due to its environmental and economic benefits [1e3]
As the LPG percentage was increased the start of combustion (SOC)
As LPG is inducted along with the air in the induction stroke, there is sufficient time to mix LPG with air in the cylinder. This leads to the formation of a readycombustible charge mixture, which is burned in the premixed combustion phase
Summary
Liquefied petroleum gas (LPG) is considered as a promising alternative fuel and has been widely used in transportation due to its environmental and economic benefits [1e3]. The high octane number of LPG makes it suitable for spark ignition engines. The low cetane number (CN) of LPG makes it difficult to be used in large proportions in compression ignition engines, mainly due to high cyclic variation [5]. The addition of cetane enhancer can improve the performance of LPG fuelled diesel engine operation [5e7]. It has been reported that with the use of in-cylinder injected LPG, improvements in smoke and nitrogen oxides (NOx) emissions are evident and in some cases carbon monoxide (CO) emission can be minimised, in high engine load [8]. The presence of the LPG spray combined with diesel fuel into the cylinder promotes diesel atomisation, increasing the velocity of diffusion combustion, which in turn diminishes soot formation [9]
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