Improving the combustion and emissions of direct injection compression ignition engines using oxygenated fuel additives combined with a cetane number improver

According to the fuel design concept, three oxygenated fuels including ethanol, dimethyl carbonate (DMC), and dimethoxy methane (DMM) were selected to mix with diesel fuel. Then, the effects of oxygen content and the cetane number of the blend fuels on diesel engine combustion and emissions were evaluated. The experiments were conducted on a four-cylinder high-speed diesel engine. The results show that, with the increase of the oxygen content in blend fuels, the ignition timing delays and the combustion duration shorten at different operating conditions, and the brake thermal efficiency improves from middle to full loads. The engine NOx emissions decreased at overall operating ranges when oxygenated fuels were added to the diesel fuel, and smoke emissions also improved for all oxygenated blend fuels except for ethanol-diesel blends at low and middle loads. In the case of the DMC-diesel blend fuel, when the oxygen content increased up to 15%, the smoke number decreased by 75%, and NOx emission improved by 15-20%. CO emissions of blend fuels decreased at large and full loads but deteriorated at lower and middle engine loads. HC emissions increase at overall operating ranges and increase much more with the increase of oxygenated fuel volume and decrease of the engine load. To solve this problem, the cetane number improver was added to the 15% ethanol-diesel blend fuel. As a result, the HC and CO emissions at overall operating ranges reduce substantially, and NOx emissions further reduce, but smoke emission maintains the same level when compared to the ethanol-diesel blend fuels without the cetane number improver. According to the heat release rate analysis, it can be found that the combustion characteristics of an ethanol-diesel blend fuel at large loads may be resumed to diesel fuel by the CN improver but that a large difference exists at lower loads.