Potential Analysis of a DMC/MeFo Mixture in a DISI Single and Multi-Cylinder Light Vehicle Gasoline Engine 2021-01-0561

In this study a mixture of dimethyl carbonate (DMC) and methyl formate (MeFo) was used as a synthetic gasoline replacement. These synthetic fuels offer CO₂-neutral mobility if the fuels are produced in a closed CO₂-cycle and they reduce harmful emissions like particulates and NO_X. For base potential investigations, a single-cylinder research engine (SCE) was used. An in-depth analysis of real driving cycles in a series 4-cylinder engine (4CE) confirmed the high potential for emission reduction as well as efficiency benefits.

Beside the benefit of lower exhaust emissions, especially NO_X and particle number (PN) emissions, some additional potential was observed in the SCE. During a start of injection (SOI) variation it could be detected that a late SOI of DMC/MeFo has less influence on combustion stability and ignitability. With this widened range for the SOI the engine application can be improved for example by catalyst heating or stratified mode. Furthermore, until λ = 0.8 no significant PN increase was noted in contrast to gasoline. This is also a positive capability for combustion modes with local rich areas in the mixture. From the experience of previous investigations, the synthetic fuels’ high knock-resistance potential enabled an increase in the compression ratio (CR) from epsilon ~ 11 to ~ 15 to enhance the indicated efficiency.

In general, in the 4CE the positive effects of DMC/MeFo on harmful emissions were confirmed. Even in the series configuration, the brake efficiency increased by 16 % at maximum low-end torque compared to gasoline. The increased in-cylinder cooling and the lower laminar flame temperature by the DMC/MeFo implies lower maximum exhaust temperatures. Therefore, a stoichiometric mixture could be used over the whole engine map. During the legislative driving cycles, for example WLTC, the PN, NO_X, CO and CH₄ emissions decreased by 50 % or more.

In summary, oxygenated fuel opens great opportunities for replacing fossil fuel in gasoline engine applications.