Analysis of experimental results with an active pre-chamber ultra-lean burn SI engine

Abstract

To ensure that private cars can continue to be used in the future, they must become significantly more efficient and at the same time emit considerably less pollutants. In addition to pure electric drives, further optimized gasoline engines in hybrid powertrain configurations still offer major potentials in this respect. A major step toward increasing efficiency can be achieved by extremely lean burn combustion. If, in addition to low fuel consumption, this operation should also simultaneously reduce NOx raw emissions, lean-burn operation with relative air/fuel ratios of λ≥ 2 must be enabled in wide ranges of the engine operation map. Within the scope of this publication, results of experimental investigations with a lean burn pre-chamber ignition system applied to a small gasoline engine with 75 mm bore and 90.5 mm stroke are presented. In this context, the effects of the pre-chamber design on emissions and fuel consumption are examined. By comparing different pre-chamber enrichments with natural gas and conventional RON98 gasoline, it can be shown that with the direct liquid injection of gasoline into the pre-chamber similar good thermodynamic results as with natural gas can be achieved with the advantage of easier integration of a single fuel system. Due to its significantly improved lean burn capability with relative air/fuel rations of up to λ = 3, combined with low specific indicated NOx raw emissions of less than 0.1 g/kWh, the presented lean-burn combustion system offers excellent conditions for further efficiency improvements of electrified powertrains. WLTP cycle simulations based on measured engine maps for the developed combustion process resulted in a fuel consumption reduction of up to 10%. At the same time, NOx raw emissions below the Euro 6d limit of 60 mg/km can be achieved.