Why Liquid Phase LPG Port Injection has Superior Power and Efficiency to Gas Phase Port Injection

This paper reports comparative results for liquid phase versus gaseous phase port injection in a single cylinder engine. It follows previous research in a multi-cylinder engine where liquid phase was found to have advantages over gas phase at most operating conditions. Significant variations in cylinder to cylinder mixture distribution were found for both phases and leading to uncertainty in the findings. The uncertainty was avoided in this paper as in the engine used, a high speed Waukesha ASTM CFR, identical manifold conditions could be assured and MBT spark found for each fuel supply system over a wide range of mixtures. These were extended to lean burn conditions where gaseous fuelling in the multi-cylinder engine had been reported to be at least an equal performer to liquid phase.

The experimental data confirm the power and efficiency advantages of liquid phase injection over gas phase injection and carburetion in multi-cylinder engine tests. Analysis shows the charge state at the end of compression is the major contributor to the performance difference. Secondary differences such as the mixture homogeneity also have an important influence. The lower temperature combustion with liquid phase LPG also delivers substantial NOx emission reduction.

Suggestions are made for overcoming the deficiency of gaseous phase injection which may be preferred as its application avoids the high cost of the high pressure in-tank LPG pump needed for liquid phase injection.