Controlled Auto-Ignition (CAI) also known as Homogeneous Charge Compression Ignition (HCCI) is increasingly seen as a very effective way of lowering both fuel consumption and emissions. Hence, it is regarded as one of the best ways to meet stringent future emissions legislation. It has however, still many problems to overcome, such as limited operating range.
This combustion concept was achieved in a production type, 4-cylinder gasoline engine, in two separated tests: naturally aspirated and turbocharged. Very few modifications to the original engine were needed. These consisted basically of a new set of camshafts for the naturally aspirated test and new camshafts plus turbocharger for the test with forced induction.
After previous experiments with naturally aspirated CAI operation, it was decided to investigate the capability of turbocharging for extended CAI load and speed range. The results show that the CAI range could achieve higher load and speed with the addition of the turbocharger. The engine showed, however, increased fuel consumption due to excessive pump losses. Emissions, although higher than in the NA CAI counterpart, have been still reduced substantially in comparison to the original SI engine. NOx levels could be reduced by up to 98% when compared to a standard SI production engine.
In order to better understand the results and find ways to improve the current set-up, engine performance and emissions were analyzed.