Residual-effected homogeneous charge compression ignition with delayed intake-valve closing at elevated compression ratio

Abstract

Residual-effected homogeneous charge compression ignition (HCCI) was investigated using a single-cylinder research engine equipped with fully-flexible variable valve actuation. Operation at elevated compression ratios was explored to determine its effect on efficiency. Results showed that efficiency is decreased significantly by advanced phasing owing to increased thermal losses. However, if combustion phasing is held fixed, elevated compression ratio operation showed little effect on efficiency. Further experiments explored the use of IVC time as a control parameter at the elevated compression ratio. Tests were conducted to determine if an efficiency benefit could be realized from increasing the compression ratio and delaying IVC to increase the extent of expansion relative to compression. No significant change in efficiency was observed, although variation in IVC timing offered significant control authority. Delayed IVC was used in conjunction with variable IVO to control independently load and phasing of HCCI at the elevated compression ratio. Tests were also conducted to assess the significance of the measured exhaust temperature on HCCI phasing. EVO was introduced as a third control parameter, along with IVO and IVC, to control independently initial mixture composition, compression work, and exhaust temperature. Results indicated that the measured exhaust temperature was not a good indicator of HCCI phasing and suggested the stabilizing role of heat transfer to the reinducted exhaust gases. Results also suggested a set of control parameters that achieve the full range of HCCI operation with minimal degrees of freedom.