AN EXPERIMENTAL INVESTIGATION OF LOW TEMPERATURE COMBUSTION REGIMES IN A LIGHT DUTY ENGINE

A continuous investigation on the improvement of internal combustion engines is necessary due to the stringent emission and fuel economy regulations. Low Temperature Combustion (LTC) is a promising field of research since it can simultaneously reduce NOx and soot while attaining high thermal efficiencies in automotive engines. A thorough study of several LTC regimes is necessary to understand the quantitative comparison and the extent of feasibility of these regimes functioning on an automotive engine. This thesis concentrates on an experimental investigation of three different LTC modes namely Homogeneously Charged Compression Ignition (HCCI), Partially Premixed Compression Ignition (PPCI) and Reactivity Controlled Compression Ignition (RCCI) on a 2.0-liter 4-cylinder gasoline engine. A detailed experimental study of the LTC regimes with over 2,500 data points on a GM 2.0 L Ecotec engine is performed to study the relationship among the engine variables, combustion and performance characteristics. The operating range extension of the engine for lean limit and load limit while functioning in each combustion mode is discussed through operating region maps. Performance metric maps for indicated specific fuel consumption (ISFC), brake specific fuel consumption (BSFC), thermal efficiency and exhaust temperature are developed and discussed. The optimized maps are developed for each LTC regime considering the best ISFC at each speed-load condition. Moreover, the behavior of the engine for each combustion mode is investigated and discussed through the trends observed for combustion phasing (CA10, CA50, CA90 and BD) and performance metrics (IMEP, indicated thermal efficiency, combustion efficiency). The results show that the RCCI combustion mode offers the best indicated thermal efficiency of 47% among the three LTC modes. The Start of Injection (SOI) of n-heptane is found as a dominant factor in order to determine the optimal combustion phasing. The results of a comparative study indicate that HCCI is more suitable for running the engine at low loads, PPCI for low-mid loads and RCCI for mid-high loads