Modelling of Crankcase Gas Behaviour in a Heavy-Duty Diesel Engine

Abstract: The origin of many environmental and health hazardous emissions from diesel engines are the crankcase gases. Since no regulations of the emission levels from the crankcase have existed in the past, no attention has been paid to cleaning crankcase gases. New regulations are coming up and they will all demand lower emissions from the engine. This has lead to the introduction of the Alfdex separator. The Alfdex separator is built to separate oil droplets and soot from the crankcase gases. In the research work made in this master thesis, we have investigated the possibilities to model the crankcase gases with respect to flow rate and oil content with some parameters of the engine. The model could then be used as an input to a controller that controls the separator speed. Since the test engine used here is old and is not in production anymore, the idea of the modelling is to find more general characteristics rather than specifics for the tested engine. The work made in this master thesis shows that the crankcase gas flow rate can be modelled in a good way. The identifying process done here is accomplished by field tests on a Volvo bus equipped with a TD123E motor, which is a 6 cylinder, 12 litres, turbocharged diesel engine. Since no prior testing had been made, the project involved much practical work such as test rig building, mounting on the bus etc. The measurements on crankcase gases have been made both at stationary modes and dynamically. The project also involves measurements of the oil content in crankcase gases. These measurements have been made at steady state, with no possibility to investigate the dynamic behaviour of the oil aerosol. The tests made on the size distribution of oil in the crankcase gases gives a hint to the future development of a controller.