Optimization of Two-Stage Combustion System Fueled by Lean-Burn Compressed Natural Gas Mixtures for Light-Duty Vehicle Engines

The search for new solutions for engine ignition systems and combustion of lean air-gas mixtures has led to the application of a two-stage combustion system, previously also known as turbulent jet ignition (TJI). In this article, the authors proposed using a pre-chamber filled with a rich ignition mixture, which is turned into an outgoing burning jet that facilitates the combustion of lean mixtures in the main combustion chamber. Various two-stage combustion systems were tested in a high-speed natural gas-powered combustion engine as a part of the Horizon 2020-GasOn (Gas-Only Internal Combustion Engines) research program. The results of testing the effectiveness of using various pre-chambers are discussed in this article. These tests were carried out in a selected engine’s operating range using three pre-chambers with different geometry. The first phase of the research concerned the selection of a gas supply system (injection on the intake valve or Heinzmann mixer). Due to better mixture homogenization in the cylinder (based on thermodynamic waveforms) with the use of a mixer (auxiliary mixture formation), the decision was made to use it further in the selection of the pre-chambers geometry. The selection of the pre-chambers was performed based on the thermodynamic and emission indicators of the combustion process. Due to the differences in results making direct comparison difficult, the use of pseudo-poly-optimization to select the pre-chamber with the best quality indicators was chosen. A pre-chamber was selected to allow lean mixtures (air excess ratio of up to 1.65) at an average combustion engine load-indicated mean effective pressure (IMEP = 7 bar).