Combustion instability and white smoke emissions under cold starting of diesel engines

More stringent regulations have been enforced over the past few years on diesel exhaust emissions. White smoke emission, a characteristic of diesel engines during cold starting, needs to be controlled in order to meet these regulations. An investigation on white smoke constituency, sources and effect of fuel properties, design and operating parameters was made. A new technique was developed to measure the gaseous hydrocarbons (HC) and solid and liquid particulates. Experiments were conducted on a single cylinder direct injection diesel engine in a cold room. The gaseous HC emissions were measured using a high frequency response flame ionization detector. The liquid and solid particulates were collected on a paper filter placed upstream of the sampling line of the FID and their masses were determined. A comparative study was made between white smoke in its three forms for diesel fuel (DF2) and jet fuel (JP8). The important parameters affecting hydrocarbon emissions were discussed. These parameters included ambient temperature, fuel properties, ignition delay and engine speed.; Combustion instability was investigated during the cold starting of the same engine. The experiments covered fuels of different properties at different ambient air temperatures and injection timings. The analysis showed that the pattern of misfiring (skipping) was not random but repeatable. The engine may skip once (8-stroke-cycle operation) or twice (12-stroke-cycle operation) or more times. The engine may shift from one mode of operation to another and finally run steadily on 4-stroke cycle. All the fuels tested produced this type of operation at different degrees. The reasons for the combustion instability were analyzed and found to be related to speed, residual gas temperature and composition, accumulated fuel and ambient air temperature.