Comparison of cycle-by-cycle variation of measured exhaust-gas temperature and in-cylinder pressure measurements

Closed-loop control of the combustion process in the internal-combustion engine on a cycle-to-cycle basis is desirable to achieve better fuel economy and reduce pollutant emissions. This work explores the possibility of monitoring the in-cylinder combustion process of a spark-ignition engine by measuring exhaust-gas temperature. A small-diameter thermocouple (25.4 μm or 0.001 in.) is inserted into the exhaust manifold to measure exhaust-gas temperature, while in-cylinder pressure is monitored with a pressure transducer. Cycle-by-cycle variations of the measured exhaust-gas temperature are compared to IMEP variation for groups of cycles. The experimental results show that coefficient of variation of maximum temperature follows the same trend as the coefficient of variation of indicated mean effective pressure. Cycle-by-cycle variation of IMEP is reflected in cyclic variation of measured exhaust-gas temperatures for operating conditions under which the engine is working at a fixed speed or load and when cyclic variability is caused by changing engine parameters such as spark timing, injection timing, and air/fuel ratio. Finally, by using a moving window covering a small number of cycles, it is possible to show that the COV trend of maximum exhaust temperature mirrors that of IMEP.