On the quantitative relationship of the in-cylinder heat to work conversion process of natural gas spark ignited engine under steady state and transient operation conditions

The performance characteristics of an automotive engine under the road operation conditions, i.e. under transient torque and power output conditions, as well as the instant in-cylinder thermal to work conversion efficiency, are very important for the vehicle’s performance and fuel economy, but difficult to measure. In an effort to identify and confirm the quantitative relationships between the engine performance parameters with controlling and operating parameters (such as the engine speed, intake pressure, lambda and so on) for natural gas spark ignited engines, the controlling equations of the in-cylinder indicated thermal efficiency and indicated mean effective pressure are derived. The results show that the derived controlling equations also demonstrate good agreement with experimental data under both steady state and transient operation conditions. This research confirms the feasibility to identify indirectly the natural gas spark ignited engine’s performance under the road conditions through analyzing the measureable or available controlling and operational parameters, and provides a method for on-line analysis and optimization of the engine operation parameters.