Abstract
Keywords - HC emissions, MVEG cycle, single-cylinder engine, transient tests, cold conditions
Abstract
HC emissions of gasoline engines are closely dependent of engine control strategies as well as of combustion chamber and fuel injection system design. If these parameters are clearly inter-correlated, strategies are often set up at a late stage of development while main parts of the design are frozen early in the development process, often after single-cylinder engine test.
In order to be able to study simultaneously the effect of design and strategies parameters at an early stage of engine development, a methodology has been set up to reproduce on a single-cylinder engine the beginning of NMVEG cycle and to analyse corresponding HC emissions. This methodology uses different fuels and analysis tools such as fast FID to assess the HC sources. It uses also engine cooling regulation to follow the thermal behaviour of multi-cylinder engine and a fast prototyping system for the engine control. Special attention has been paid to take into account the acoustic effect on the air feeding of the engine.
A complementary study on emissions during stabilised conditions met on the MVEG cycle offers the ability to go further into HC sources analysis with the use of 4 fuels methodology and fast FID measurements.
The results show that transient tests keep main tendencies observed during stabilised conditions. Wall wetting appears as the main source of HC emission in case of direct injection. A trade off between mixture preparation duration and fuel impact on the piston is emphasised. Optimal injection timing is different with hot or cold conditions. Transient effects are especially sensitive during cold conditions. Main conclusions could be obtained with a simplified methodology based on warm-up phase reproduction at constant speed and load, with different fuels.