Improvement of diesel engine startability under low temperatures by vortex tubes

Cold start is one of the most problematic combustion phases for diesel engines. During this phase, a large proportion of pollutants are produced within the cylinder due to misfiring and incomplete combustion due to the low engine temperatures. Furthermore, exhaust after-treatment devices work inefficiently since their minimum operation temperatures cannot be reached. In addition to this, at temperatures below 0 °C the possibility of continuous misfiring could actually impede the engine start. Ambient temperature is one of the most important factors affecting the diesel engine cold startability. The aim of this study is to improve diesel engine startability under low temperatures by vortex tubes. A vortex tube was used to increase the intake air temperature in a six cylinders, four stroke and direct injection diesel engine of a truck. The hot air obtained from the hot outlet of the vortex tube was mixed with the air coming from the inlet of the intake manifold and the warmer air was sent to the cylinders. The compressed air required for the operation of the vortex tube was provided from the air tank of the compressed-air brake system of the truck. The effects of variation in ambient temperature on the engine cranking speed and in-cylinder pressure were analyzed and presented. Experiments were conducted for ambient air temperatures of -5, 0 and +4°C. It was found that the reduction in ambient temperature resulted in prolonged cranking periods along with the longer time taken to reach idling speed as well as increased combustion instability for the engine without vortex tube. The use of the vortex tube increased the intake air temperature, which decreased durations of engine starting-cranking, cranking-idling, and idling-stabling. These results indicate that the cold starting performance of the diesel engine could be improved by using vortex tubes.