Abstract
The effect of the fuel injection ratio on the combustion and emission characteristics of stratified lean mixture combustion was investigated for a spray-guided liquefied petroleum gas (LPG) direct injection engine. Inter-injection spark-ignition combustion—a specially designed combustion strategy for LPG fuel derived from a two-staged injection—was employed to maximize the improvement in thermal efficiency when combustion stability is secured. When changing the fuel injection ratio, the optimum spark advance and fuel injection timings were experimentally determined to maximize the thermal efficiency based on sweeping timings. The optimum fuel injection ratio with the highest thermal efficiency (42.76%) and stable operation was 60%/40%, with the optimization of the spark advance and fuel injection timing, because of the locally rich mixture region in the recirculation zone. NOx emissions were at their highest level with a fuel injection ratio of 60%/40% because of the high combustion temperature, and the levels of total hydrocarbon and CO emissions with 50%/50% and 60%/40% fuel injection ratios were similar, whereas emissions at 70%/30% were significantly higher because of fuel wetting and the formation of over-lean mixture.
Highlights
Given the recent rise in oil consumption combined with global concerns regarding greenhouse gas accumulation and fossil fuel depletion, researchers are attempting to develop technologies to enable low carbon dioxide (CO2 ) emissions and low fuel consumption [1,2]
In [16,17], we evaluated the effect of the split-injection strategy and analyzed the lean combustion characteristics of a spray-guided direct-injection combustion system
One of the main objectives of this study is to evaluate the effects on engine performance and emission characteristics due to different liquefied petroleum gas (LPG)-stratified lean combustions close to the lean-burn stability limit
Summary
Given the recent rise in oil consumption combined with global concerns regarding greenhouse gas accumulation and fossil fuel depletion, researchers are attempting to develop technologies to enable low carbon dioxide (CO2 ) emissions and low fuel consumption [1,2]. As controlling the intake air amount increases the fuel consumption because of the occurrence of pumping loss, the high specific fuel consumption must be reduced to the level of the compression-ignition diesel engine. The use of lean combustion can be an alternative to solve the problem of high fuel consumption and exhaust gas emissions. Since liquefied petroleum gas (LPG)—a low-carbon gas fuel—has the potential for reducing emissions and improving fuel economy, ultra-lean LPG direct injection engine technology has attracted attention. Boretti et al [4] presented a computer model for analyzing direct injection engines with spark ignition and reported that specific fuel consumption might be reduced through LPG-stratified lean combustion.
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