Low Temperature Combustion Strategies for Compression Ignition Engines: Operability limits and Challenges

Low temperature combustion (LTC) strategies such as homogeneous charge compression ignition (HCCI), smokeless rich combustion, and reactivity controlled compression ignition (RCCI) provide for cleaner combustion with ultra-low NOx and soot emissions from compression-ignition engines. However, these strategies vary significantly in their implementation requirements, combustion characteristics, operability limits as well as sensitivity to boundary conditions such as exhaust gas recirculation (EGR) and intake temperature. In this work, a detailed analysis of the aforementioned LTC strategies has been carried out on a high-compression ratio, single-cylinder diesel engine. The effects of intake boost, EGR quantity/temperature, engine speed, injection scheduling and injection pressure on the operability limits have been empirically determined and correlated with the combustion stability and performance metrics. For dual-fuel combustion of diesel-ethanol (RCCI), the pilot-to-main fuelling ratio and pilot timing/quantity variations have been investigated to identify high-efficiency or high-load operation. The factors affecting the real-world application of these LTC strategies have been identified, the challenges needed to overcome have been highlighted and their effects on the engine performance quantified.