Experiment of cetane number improver on emissions of diesel engine fueled with methanol/biodiesel

Methanol and biodiesel are the oxygenated alternative fuels of diesel engine, which can effectively reduce particulate emissions of diesel engines. However, due to the low cetane number of methanol, it is difficult for methanol to ignite in diesel engine. The addition of cetane number improver is an effective method to improve the ignition performance of diesel engine fuels. In order to study the effects of different cetane number improvers on diesel engine emission pollutants, three kinds of cetane number improvers, such as alkyl nitrates, naphthyl nitrates and ethers were chosen and added to the methanol / biodiesel blend fuel with the mixing ratios of 0.3%, 0.3%, and 3%, respectively. The effects of the cetane number improvers on the physical and chemical properties of methanol/biodiesel blend were investigated. The engine bench test was carried out on the 186F diesel engine without adjusting the structure of the diesel engine during the test. The in-cylinder pressure and exhaust temperature of the diesel engine fueled with methanol/biodiesel blend was measured at 1 800, 3 000 r/min, 25%, and 100% load, then the ignition delay and combustion duration were calculated. The variation of pollutants such as HC, CO, NOX and smoke emitted from the diesel engine at 1 800 and 3 000 r/min, 10%, 25%, 50%, 75% and 100% loads were measured. The effects of cetane number improvers on diesel engine exhaust pollutants were investigated. The results showed that the addition of cetane number improvers had little effects on the density, viscosity and other physical and chemical properties of the methanol/biodiesel blend, but the cetane number of the blend was obviously increased. Because of the low decomposition activation energy of the cetane number improvers, the improvers can help the blend to shorten the chemical delay period. With the addition of cetane number improvers to the methanol/biodiesel blend, the in-cylinder pressure peak was increased, the ignition delay was shortened, and the combustion duration was prolonged. In addition, the corresponding crankshaft angle of in-cylinder pressure peak was advanced. When the amount of improvers was equal, the ignition delay period of alkyl nitrates mixture was the shortest among the three cetane number improvers. When the diesel engine changed from 25% load to 100% load, the exhaust temperature was increased by 194-235 K at the same speed. While the diesel engine speed had smaller effects on the exhaust temperature and the variation range was ?3.24%-3.45%. With the addition of cetane number improvers, the HC and CO emission were increased, especially at higher engine load. However, the addition of cetane number improvers can reduce the NOX and the smoke. When the diesel engine was at 3 000 r/min, 100% load, NOX was reduced by 12.90%, 6.45%, 3.87% with the addition of alkyl nitrate, naphthenic nitrates and ethers respectively, and the smoke was reduced by 11.76%, 17.65%, 38.24%. The addition of cetane number improver in methanol/biodiesel blends not only can improve the ignition characteristics of the fuels, but also reduce NOx and particulate emissions.