Combustion sensitivity to the nozzle hole size in an active pre-chamber ultra-lean heavy-duty natural gas engine

Abstract

Abstract Active pre-chamber configurations are considered a valuable solution for improving the operation of the internal combustion engine, in the view to overcome the many challenges it has been made to face. Combining this technology with the use of natural gas, a fuel that has increasing availability and interest in the market share, it is possible to burn ultra-lean mixtures (with air-to-fuel ratios, λ greater than 1.5) delivering reduced emissions and fuel consumption, without compromising efficiency and stability requirements. In this work three pre-chamber nozzles differing for the orifice diameter were tested in a stationary heavy-duty 6-cylinder engine (originally a compression ignition) converted to work with a single cylinder and spark ignition operated. An extensive test matrix was carried to perform spark timing, global lambda and load target sweeps in order to assess the behaviour of the three nozzles with respect to the changing operating conditions. Analysis of in-cylinder pressure traces and heat release rate have allowed to unveil the characteristics of the combustion phasing starting from the pre-chamber to the development in the main chamber, relating these to the performance of the engine in terms of emissions, efficiency and stability.