An investigation of icing in a liquid petroleum gas liquid phase fuel injector with a shut-off valve

Abstract

Liquefied petroleum gas (LPG) engines are considered to be a clean energy source. The fuel supply strategy for this type of engine is moving away from a mixer-type fuel supply and towards an LPLI (liquid phase LPG injection) system, which injects liquid phase LPG directly into the manifold, enhancing volumetric efficiency, giving a faster response, and providing more precise fuel control. The LPLI system requires a new development to meet more stringent emissions regulations than previous regulations. This new development is motivated by the tendency of LPG in an LPLI system to leak out of the injector after the engine is shut off. Installing a shut-off valve directly after the injector is one possible strategy for preventing this leakage. To install the shut-off valve in the injector, it is necessary to change its structure. In a prototype of the shut-off valve type injector, the fuel path inside the adapter becomes longer and more complicated than in a conventional LPLI injector, which may cause icing at the injector tip. Because LPG absorbs heat for evaporation when it is injected into the manifold, the temperature of the injector tips is decreased to a temperature even below freezing. Water vapour in the intake air passing the cold injector can form ice that sticks on the surface of the injector. This phenomenon is called icing and can become disruptive to precise air/fuel control as ice particles fall off and enter the cylinder. Using injection visualization, emissions analysis, and data on engine running conditions, these icing phenomena are classified into two types: one at the cold adapter surface and the other at the LPG transfer tube (a Teflon tube) tip, which is placed in the centre of the injector adapters. The icing phenomena in shut-off valve type LPLI injectors are significantly reduced by enhancing heat transfer between the cold injector tip and the hot intake manifold, and by surrounding the injecting tip with a shroud.