Impact of turbocharging on the startability of diesel engines in winter
The article explores the startability of diesel engine with and without turbocharger under cold conditions. It is known that under subzero temperatures typical for many regions of Russia, the startability of diesel engines is significantly deteriorated. The aim of research is to study the impact of supercharger on startability of diesel engines. In the process of experimental researches by means of light-beam oscillograph, the indices characterizing the starting sequence have been received, namely: rotational frequencies of crankshaft and turbocharger rotor, air output, time of starting, cylinder pressure. It is found that the startability of engine with supercharger conforms to the state standard requirements at the temperature of 8 degrees C below zero, whereas the startability of engine without supercharger conforms to these requirements at 12 degrees C below zero. The starting time of turbocharged engine is extended due to the resistance in inlet line, that leads to increase of inlet manifold vacuum, to decrease of final compression pressure and therefore to decrease of maximum cylinder pressure. The article determines the operation modes of turbocharger at the starting time and at post-launch warm-up. It is found that operating in these modes leads to the shortage of oil in turbocharger bearing under cold conditions. The research has shown that turbocharger mounted on the engine causes the significant reducing of delivery ratio, and therefore the deterioration of startability. Sustainable startability is possible with installation of circulation valve on engine inlet manifold or compressor, and also with use of turbocharger that can be switched off. It is found that turbocharger can operate in the mode of oil starvation at the beginning of post-launch warm-up under cold conditions. In order to reduce the wear of sleeve-shaft coupling, it is recommended to change the current scheme of oil filling or the design of turbocharger to provide oil inlet directly to turbocharger bearings in the moment of starter switching-on.