LPG and Prechamber as Enabler for Highly Performant and Efficient Combustion Processes Under Stoichiometric Conditions

The European Union has defined legally binding CO2-fleet targets for new cars until 2030. Therefore, improvement of fuel economy and carbon dioxide emission reduction is becoming one of the most important issues for the car manufacturers. Today's conventional car powertrain systems are reaching their technical limits and will not be able to meet future CO2 targets without further improvement in combustion efficiency, using low carbon fuels (LCF), and at least mild electrification. This paper demonstrates a highly efficient and performant combustion engine concept with a passive pre-chamber spark plug, operating at stoichiometric conditions and powered with liquefied petroleum gas (LPG). Even from fossil origin, LPG features many advantages such as low carbon/hydrogen ratio, low price and broad availability. In future, it can be produced from renewables and it is in liquid state under relatively low pressures, allowing the use of conventional injection and fuel supply components. To take advantage of the specific capabilities of LPG a combustion system is designed to increase combustion efficiency and decrease fuel consumption and engine-out emissions. The applied combustion chamber geometry, including the passive pre-chamber, leads to lower exhaust gas temperatures and consequently higher peak power when operating under stoichiometric conditions. The presented combustion system was developed by means of extensive 3D-CFD simulations and experimental single-cylinder engine results by applying advanced combustion diagnosis and analysis tools. The potential of the combustion system is demonstrated over the entire engine map focusing on certification and real operating conditions such as idle, low load and maximum power. The potential of the combustion process will be figured out, both for low and high-power densities, with respect to future emission limitations.