Cold Start on Diesel Engines: Effect of Fuel Characteristics

Faced with the need to reduce greenhouse gas emissions, Diesel engines present the advantage of having low CO 2 emission levels compared to spark ignited engines. Nevertheless, Diesel engines still suffer from the fact that they emit pollutants and, particularly nitrogen oxides (NOx) and particulates ( PM). One of the most promising ways to meet this challenge is to reduce the compression ratio (CR). However a current limitation in reducing the diesel CR is cold start requirements. In this context, the fuel characteristics such as the cetane number, which represents ignition, and volatility could impact cold start. That is why a matrix of 8 fuels was tested. The cetane number ranges from 47.3 to 70.9 and the volatility, represented by the temperature necessary to distillate 5% of the product (T5%), ranges from 173 to 198 degrees C. The engine tests were carried out at - 25 degrees C, on a Common rail 4-cylinder Diesel engine. Two engine configurations were studied: a nominal CR of 16:1 and a reduced CR of 14:1. Operating points were run with the same settings for all the fuels. Moreover a statistical analysis of the results was used in order to highlight the fuel impacts on cold behaviour (start and idle). The main results show that the difference between tests operated with CR equal to 16:1 and 14:1 appears only during the idle phase. The impact of volatility is not clear, but the increase in cetane number means better performances on cold start.