Piston Fuel Film Observations in an Optical Access GDI Engine

Abstract

Increasing pressure for reduced fuel consumption, particularly in Japan and Europe, has motivated the development of various engine concepts that improve part-load efficiency. One of these concepts is Gasoline Direct Injection, or GDI. By injecting fuel under high pressure directly into the combustion chamber later in the engine cycle and using various piston geometry and combustion chamber airflow techniques, a locally stratified, globally lean mixture can be used to obtain part load power with greater efficiency. Emissions concerns, however, particularly hydrocarbons from unburned mixture and liquid films on the piston and cylinder walls, are a major concern.The purpose of this project was to observe the interaction of a GDI fuel spray with the moving piston crown in an optical access engine, describe the interaction qualitatively, devise a means to measure the residual fuel film on the piston quantitatively, and compare the results with a Computational Fluid Dynamics (CFD) simulation. CFD was also used extensively to aid in the design of the experimental apparatus, particularly in selecting the spray and injection parameters that would allow stratified charge operation in the simple geometry available in the optical engine.The CFD simulations predicted that within the operating window for stratified charge operation, between 1% and 4% of the injected fuel would remain on the piston as a liquid film. The most influential parameter for the quantity of residual fuel film was the piston temperature. The experimental results support the CFD simulations qualitatively, but the amount of fuel film remaining on the piston is under-predicted. High-speed video footage shows a vigorous spray impingement on the piston crown resulting in vapor production. The primary GDI combustion process, a roughly premixed flame, is followed by a turbulent diffusion flame or "pool fire" in the region of the liquid film once the piston is warm enough to produce vapor at a high enough rate. Thanks also go to my family, for creating and shaping me as I am, the people who helped me get into MIT including

Comparisons of Laboratory and On-Road Type-Approval Cycles with Idling Emissions. Implications for Periodical Technical Inspection (PTI) Sensors

“…This leads to incomplete fuel evaporation due to the limited time available for fuel and air mixing, resulting in localized rich combustion and PM formation [ 55 ]. Additionally, a small amount of fuel may impinge on the piston and make direct contact with the cold cylinder walls, which may lead to diffusion combustion and subsequent PM formation [ 56 ], in particular during fuel enrichment events. Thus, it seems that the idle concentrations cannot “represent” the fuel enrichment events of the GDI engines.…”

Size distribution, chemical composition and oxidation reactivity of particulate matter from gasoline direct injection (GDI) engine fueled with ethanol-gasoline fuel

“…It inevitably results in some regions with high temperature but insufficient oxygen in the cylinder, and this condition leads to significant endothermic pyrolysis reactions which contribute to soot formation. Second, as the fuel is injected, a certain amount of fuel in spray may impinge on the piston [8]. Due to the high temperature of piston surface, the fuel evaporates quickly and forms a vapor film, which has much higher heat transfer resistance than the liquid.…”

European Regulatory Framework and Particulate Matter Emissions of Gasoline Light-Duty Vehicles: A Review

“…On the other hand, in GDI engines, fuel is sprayed directly into the combustion chamber, which leads to incomplete fuel evaporation due to the limited time available for fuel and air mixing, resulting in localized rich combustion and particulate matter (PM) formation [42,43]. Additionally, a small amount of fuel may impinge on the piston and make direct contact with the cold cylinder walls, which may lead to diffusion combustion and subsequent PM formation [44]. Wall-wetting can induce the formation of a solid nucleation mode consisting of ash derived from metallic lubrication oil additives [45].…”