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
NOX. 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 NOX 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, NOX, CO and CH4 emissions decreased by 50 %
or more.
In summary, oxygenated fuel opens great opportunities for replacing fossil fuel
in gasoline engine applications.
