Spark-Assisted Alcohol Operation in a Low Heat Rejection Engine

This work demonstrates how the performance of a standard spark-assisted alcohol engine can be improved by using the Low Heat Rejection (LHR ) concept. The improved combustion is attained by better using the greater heat energy in the combustion chamber of a LHR engine - in this case for the faster vaporisation and better mixing of the alcohol fuels.

For this program the LHR engine used has a single cylinder diesel and alcohols sued as sole fuels were ethanol and methanol. For spark assistance an extended electrode spark plug was used and location and projection were optimised for best results. These configurations were evaluated for performance and emissions with and without LHR implementation.

The results show that the engine with LHR, ethanol fuel and spark assistance has the highest brake thermal efficiency with the lowest emissions. The implementation of LHR in the standard spark assisted engine were found to increase the brake thermal efficiency at the rated power conditions for ethanol and methanol operations by 3% and 2.5% respectively. With the LHR the hydrocarbon emission levels for both alcohols were found to be considerably decreased, showing a reduction of 200 to 300 ppm spread over the entire load range at the rated speed. However these emissions were still unfavourable at part load operation as compared to those with the baseline diesel configuration. Ultimately the cost of LHR implementation coupled with the other aspects of the engine configurations would have to be weighed against these improvements obtained in performance and emissions for a practical implementation.