Understanding HCCI characteristics in mini-HCCI engines
Master Thesis
2008
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University of Cape Town
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Abstract
This study examines the successful use of Homogeneous-Charge, Compression-Ignition (HCCI) combustion in a standard issue model-aero “diesel” engine. This two-stroke engine, unlike the more common glow-plug versions, operates without any form of combustion initiator. The fuel and air are premixed using a simple carburettor and ignited by piston compression only. The engine therefore operates in HCCI-mode even though it is referred to as a “model diesel engine”. Of particular interest is the fact that the engine is easily started from cold, warm and hot conditions. It runs stably from idle to over 11000rpm and is shown to run at high load points across the speed range with extremely conservative pressure rise rates. Furthermore, this engine is shown not to exhibit any knocking (high pressure oscillations) within its normal range of operation. The speed-load operational envelope of the engine is mapped out using a range of propellers and a propeller speed-load calibration rig. Air/fuel ratio, inlet air and exhaust gas temperatures are examined within this operational envelope. Areas of unstable operation and extremities in stable operation are also mapped out and discussed. The engine’s use of inlet throttling, crankcase pumping and residual exhaust gas metering is modelled and discussed. In addition, the engine’s inherent ability to maintain constant combustion phasing over varying operating conditions is also investigated.
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Collair, K. 2008. Understanding HCCI characteristics in mini-HCCI engines. University of Cape Town.