The Characteristics of a Heavy-Duty Engine for City Bus with Liquid Phase LPG Injection System under Various Operating Conditions

摘要

A heavy-duty LPG engine has been made with a diesel engine using liquid phase LPG injection (hereafter LPLI) system. The reason why the LPLI system used in an engine is that it has been revealed to generate higher power, higher efficiency, and lower emission characteristics than the conventional mixer type. As a fundamental study on the LPLI system application to heavy-duty engine, engine output and combustion performance were investigated with various operating conditions using a single cylinder engine. Especially, to avoid the knocking in the heavy-duty SI LPG engine due to large combustion chamber, five different swirl flows and various combustion chambers were investigated for fast burn with high turbulence level. Experimental results revealed that no problems were occurred in application of LPG fuel to the heavy -duty engine. The LPLI engine could normally operate under λ=1.5 or EGR 30% condition under stable combustion. The optimized swirl ratio for the heavy duty LPG engine was found around Rs =2.0. An oil spot method result showed that high swirl ratios above 2.3 made a disadvantage in breaking swirl flow into small turbulence scale. Among the combustion chamber cavities of bathtub, ellipse, double ellipse and nebula type, the performance of nebula type showed high efficiency and engine output under lean mixture conditions.