Abstract: To evaluate the combustion characteristics of a two-stroke glow-plug ignition miniature Internal Combustion Engine (ICE), a test platform was constructed and combustion diagnoses were implemented. Analogy analysis with conventional Gasoline Engines(GEs) shows that miniature ICE has lower Rate of Heat Release(ROHR), higher cyclic variations and longer combustion duration, about 20 °CA longer than those of conventional GEs. Besides, miniature ICE has lower indicated mean effective pressure (p_mi) and combustion pressure. Due to the unstable ignition of glowplug, the Start of Combustion (SOC) fluctuates considerably, leading to micro combustion instability. Transient analysis based on the captured first combustion cycle shows that high residual gas fraction of miniature ICE is the primary reason for the poor combustion characteristics of micro combustion. Without residual gas(the first combustion cycle), the ROHR curve of miniature ICE approaches those of conventional GEs and the combustion duration is approximately 22 °CA, nearly 50% shorter than those of stable combustion. Both engine block temperature and the residual gas affect the SOC and combustion duration, but the residual gas is the main factor. The more amount of residual gas and the higher the engine block temperature, the lower the p_mi because that both of them impair the increase of intake charge. At 150 ℃, the p_mi in steady combustion state is merely 0.17 MPa.

Key words: power mechanical engineering, vehicle engineering, miniature internal combustion engine(ICE), glow-plug ignition, combustion characteristics, residual gas