NOx reduction approach in LHR diesel engine running on biodiesel blends

Higher NOx is a major problem in a low heat rejection diesel engine running on biodiesel blends due to high combustion temperature and higher oxygen content in the biodiesel. To comply with future emission regulations, particularly dramatic decrease in NOx emissions, technology needs to keep upgrading; the reduction of the volumetric compression ratio is one of the most promising ways to allow a simultaneous increase in power at full load and NOx trade-off improvement at part load. The change of combustion chamber volume is the result of shifting the cylinder block and cylinder head assembly perpendicularly to the crankshaft axis. In consequence, the compression ratio can be varied from 1:18 to 1:12. This study describes an alumina (Al2O3) coated diesel engine running on rice bran methyl ester blends have been found experimentally by reducing the compression ratio from 18 to 15 and the results were compared to those obtained from an uncoated diesel engine with fixed compression ratio (17.5). Satisfactory performance and better emission were obtained at a compression ratio of 17. At this compression ratio, the reduction of NOx emission was observed as 9.4% for blend20 and 7.2% for blend40 with a minimum decrease in brake specific energy consumption of 3.7% for blend20 and 2.2% for blend40. An increase in brake thermal efficiency was observed as 3.5% for blend20 and 2.5% for blend40 when compared to fixed compression ratio (17.5) of uncoated engine with diesel fuel operation.