Passive pre-chamber ignition combustion and performance analys
Examensarbete för masterexamen
Mobility engineering (MPMOB), MSc
This study investigates the possibility of using a passive pre-chamber as a primary ignition source in an experimental single-cylinder gasoline-powered engine under stoichiometric conditions. The engine utilizes the Miller cycle and has the same bore and stroke dimensions to the production engine Aurobay VEP Gen3 LP, with modified cylinder head and piston resulting in a compression ratio of 13.45:1. Three Tenneco passive pre-chambers with different jet orientations were tested and com pared against each other and a baseline spark plug. To evaluate the setups fuel efficiency and emissions, a minimap consisting of 11 operating points was generated by power-weight averaging the WLTP cycle. A VVT sweep was conducted to find the optimal camshaft phasing for each setup and operation point except one. The minimap was repeated three times over three consecutive days to assess the setups repeatability and robustness, and performance comparisons were made. A WOT (Wide Open Throttle) test was conducted to compare the setups full-load perfor mance. This was complemented with a heat loss test, were one minimap run was conducted with all the setups running with the same input settings, including com bustion phasing, camshaft phasing and mass airflow. Additionally, a cooled-EGR test was conducted to investigate the potential of reducing in-cylinder heat transfer losses using external cooled-EGR. The WOT test and minimap cycling revealed three regions for the pre-chamber setups. During high load operation, a region dubbed as the "High Load Gain" re gion was identified, where the ability to advance combustion phasing resulted in a reduction in fuel consumption. On the other hand, during part load operation, a region dubbed the "Excess Heat Loss" region was observed, where the short com bustion duration and inability to advance combustion phasing resulted in excessive in-cylinder heat losses. However, with the aid of cooled-EGR, these heat losses could be effectively reduced, leading to an increase in fuel conversion efficiency. Finally, the "Low Load Balanced" region was identified, where the total heat losses between the setups became comparable. This was mainly due to the pre-chamber setups advanced VVT settings, which trapped internal-EGR and reduced the in-cylinder heat losses adequately enough to be offset by the exhaust heat losses, resulting in comparable heat losses between all of the setups. The tests concluded that the performance differences between the pre-chambers were minimal, with the simplest pre-chamber performing equally well as the rest. How ever, the performance difference between the pre-chamber and the baseline spark plug was substantial, with the pre-chamber outperforming the spark plug in re peatability, robustness, and fuel consumption in almost every test conducted, with the highest gain in fuel consumption observed at high load, with the reduction ex ceeding 6%. Therefore, the results of this thesis strongly suggest that pre-chamber technology has great potential for application in future Aurobay engines and is a promising avenue for future research and development.