Scavenged Pre-Chamber Volume Effect on Gas Engine Performance and Emissions

This work presents development and results of experimental and numerical investigations of an advanced ignition system with a scavenged pre-chamber for a natural gas fueled engine with a bore of 102 mm and stroke of 120 mm. Two combustion concepts are taken into account. The lean burn concept is used to minimize engine out emissions of nitric oxides (NOx) and to achieve high thermal efficiency at low load. The in-house designed scavenged pre-chamber enables the engine to be operated up to the air-excess ratio (lambda) of 2. A stoichiometric (lambda=1) operation is also possible. It is compatible with a three-way catalyst concept, at high load and potentially transient modes and can provide as high as possible engine power density. The influence of the scavenged pre-chamber volume on the combustion and performance within the range of the operational points of the naturally aspirated engine is presented in this paper. The two pre-chambers with different volume (2.2 % and 4.6 % of compression volume) were tested at steady state conditions.

Experimental work was complemented with CFD simulations for detailed explanation of the physics inside the main combustion chamber and in the pre-chamber. The 3-D CFD model of the experimental engine was built in AVL Fire software. The size of the pre-chamber was tested as well to verify CFD mode performance versus experimental data. Both mentioned configurations were tested numerically using multi-cycle LES calculations. These results are analyzed in terms of mixture homogeneity, rate-of-heat-release and cycle-to-cycle variability.