This study provides an overview of injector design adaptations and fuel pressure variations for oxygenated synthetic fuels, benchmarked against gasoline. The promising oxygenated fuels exhibited reduced emissions, especially with respect to particles. In gasoline engines, high fuel pressures are needed to keep the particle emissions below the permitted level. In oxygenated fuels, high fuel pressures are required to compensate for the lower volumetric energy density when used with non-adapted injectors. This study demonstrates that an adapted injector design enables engine operation with a fuel pressure reduction from 35 MPa to 10 MPa, without emission drawbacks.
The fuel investigated contained dimethyl carbonate (DMC) and methyl formate (MeFo). The fuel mass contained around 50% oxygen. A relatively high percentage of 35 vol.% MeFo was chosen because of its high vapor pressure, thus providing fast mixture formation and enabling very late compression stroke injections. The basic design adaptations are expected to be transferable to other oxygenated synthetic fuels, e.g., containing methanol (MeOH) and MeFo.
The main tests were conducted on a single cylinder research engine, based on a four-cylinder automotive engine. The exhaust gas composition was measured using an FTIR equipped with a fuel-tailored evaluation method, several standard exhaust gas analyzers, and a solid particle counting system with 10 and 23 nm cut-off sizes. The spray from both the two synthetic fuel injectors and the standard injector was further investigated at a spray chamber by means of a high-speed camera. Given a standard injector the spray pattern of 65vol% DMC+ 35vol%MeFo, and 85vol%MeOH+15 vol% MeFo were compared to the pattern of G100. All of the injectors were further investigated at an injection rate analyzer in order to provide necessary information about the injected fuel mass.