Advanced Combustion for Improved Thermal Efficiency in an Advanced On-Road Heavy Duty Diesel Engine

For internal combustion engines, the compression ratio (r) is defined as the ratio of volume at bottom dead center to the volume at top dead center and is a fundamental design parameter influencing the thermodynamic operation of the modern combustion engine. Thermodynamic cycle analysis can show that thermal efficiency increases as the compression ratio increases. An increase in the compression ratio changes the cycle such that peak compression pressure and temperatures are increased resulting in subsequent increases in the peak combustion pressure and temperature. Since the average temperature of heat addition is increased in the cycle, the thermal efficiency would theoretically increase as long as both cycles had the same heat rejection processes. These changes in peak pressure and temperature of the cycle must also be evaluated in terms of anticipated increases in engine friction and changes to the combustion duration respectively. In order to test the thermodynamic theory on actual combustion processes present in an advanced combustion engine compression ignition engine, the study of increasing the compression ratio from 20.5 to 23.5 was performed in order to understand the sensitivity and potential to increase the engine’s brake thermal efficiency (BTE). The testing and analysis completed will highlight engine efficiency, indicated cycle responses, and combustion responses to the increased compression ratio in contrast to an accompanying thermodynamic analysis.