A Technical Review on Low Speed Pre Ignition in Turbocharged Gasoline Direct Injection Engines

The current market demand and ever tightening global legislation mandate automotive OEMs to improve vehicle fuel consumption and reduce carbon based emissions. One approach to do so is by downsizing of gasoline engines. The reduced engine displacement causes lesser pumping and frictional losses and lower gas to wall heat transfer making engine more efficient. While downsizing an engine can enhance fuel economy it also brings down the power output. The power lost can be compensated by integrating a turbocharger to the engine to increase the boost pressure however, this again may create an abnormal combustion event known as low-speed pre-ignition (LSPI). The increase of pressure and temperature inside the combustion chamber at high loads also leads to a pre-ignition induced super knock and in severe cases, LSPI leads to broken piston rings, damaged pistons and bent connecting rods. Thus LSPI has become a great concern since it operates in a very common driving pattern of rapidly accelerating the vehicle at lower speed range, thereupon limiting further downsizing of gasoline engines. The present review paper comprehends the details the conditions for occurrence of LSPI mainly focusing on cause and effect of the local auto ignition taking place inside the cylinder due to formation of contaminants entering from the top land crevice during blow-down and washed from the cylinder walls during direct injection wall impingement, the parameters effecting it and various methods to mitigate the LSPI issue in turbo charged gasoline direct injection engines.