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Date of Award


Document Type

Master's report

Degree Name

Master of Science in Mechanical Engineering (MS)

College, School or Department Name

Department of Mechanical Engineering-Engineering Mechanics

First Advisor

Scott A. Miers


Fuel injection in a direct injection engine can result in liquid fuel reaching the piston surface thereby causing piston wetting. This is referred to as spray fuel impingement on the piston surface. High piston surface temperatures can aid in the vaporization of impinging liquid fuel resulting in increased air-fuel homogenization. However, increased impingement with increased engine operation results in the formation of a fuel film over the piston surface. The fuel no longer evaporates resulting in decreased performance, and unburned hydrocarbon and smoke emissions. Therefore, it is important to control fuel impingement onto the piston surface. This report details a method of identifying fuel spray impingement on the piston surface with the aid of instantaneous piston temperature measurements. The rate of change of temperature with respect to crank angle position was computed from the temperature measurements in order to identify impingement at various thermocouple locations on the piston.

The primary objective of this report is to study the effects of fuel impingement on engine performance in a direct injection, spark ignition engine. The effects of fuel impingement on parameters like brake specific fuel consumption, indicated mean effective pressure, coefficient of variation of gross indicated mean effective pressure, lowest normalized value of gross indicated mean effective pressure, and 50% mass fraction burned at various operating points was studied to emphasize the importance of optimizing injection timing in direct injection systems to enhance engine performance.

Fuel impingement was achieved via advancing start-of-injection timing very early into the engine cycle at various speed-load operating points. Engine performance was seen to improve until fuel impingement became significant onto the injection surface. Advancing start-of-injection timing past a certain optimum point, based on the speed-load condition, resulted in increased fuel consumption, decreased work output from the engine, and higher combustion variability.