In order to decarbonize and lower the overall emissions of the transport sector, immediate and cost-effective powertrain solutions are needed. Natural gas offers the advantage of a direct reduction of carbon dioxide (CO2) emissions due to its better Carbon to Hydrogen ratio (C/H) compared to common fossil fuels, e.g. gasoline or diesel. Moreover, an optimized engine design suiting the advantages of natural gas in knock resistance and lean mixtures keeping in mind the challenges of power density, efficiency and cold start manoeuvres.
In the public funded project MethMag (Methane lean combustion engine) a gasoline fired three-cylinder-engine is redesigned based on this change of requirements and benchmarked against the previous gasoline engine. A new combustion chamber design, including modified piston bowls for high compression ratio, a cylinder head with tumble intake ports, a direct gas injection and an active prechamber ignition system are the centrepieces of the new combustion system.
One of the greatest challenges is the integration and packaging of the active prechamber in the cylinder head as well as their impact on the cooling system. The additive manufacturing of the cylinder head and the active prechamber corpus offer a maximum level of design flexibility.
The outlined cooling system follows an innovative design approach by fully splitting it in two separate coolant jackets, one for the cylinder head and another for the prechamber. This split enables flexible conditioning of the prechamber corpus wall to the desired temperature level for the current engine operating point, as well as the warming up of the prechamber corpus for cold start manoeuvres. Additive manufacturing enables the integration of cooling channels in the prechamber corpus itself to directly cool potential hot spots. This results in tendency towards lower nitrogen oxide (NOx) emissions and reduced risk of undesired glow ignitions at high load points of the engine.