Engine Operation Strategies for the Alternative Diesel Fuel Oxymethylene Ether (OME): Evaluation Based on Injection Rate Analyzer and 0D-/1D-Simulation 2021-01-1190

Polyoxymethylene dimethyl ethers (OME) are promising alternative diesel fuels with a biogenic or electricity-based production, which offer carbon neutral mobility with internal combustion engines. Among other e-fuels, they stand out because of soot-free combustion, which resolves the trade-off between nitrogen oxide (NO_x) and soot emissions. Additionally, long-chain OME have a high ignitability, indicated by a cetane number (CN) greater than 70. This opens up degrees of freedom in the injection strategy and enables simplifications compared to the operation with fossil diesel. This study investigates the hydraulic behavior of two solenoid injectors with different injector geometry for heavy-duty applications on an Injection Rate Analyzer (IRA) in diesel and OME operation. For OME, both injectors show longer injection delays in all injection pressure ranges investigated, increasing with rail pressure. However, these delays are less than two degrees of crank angle in the speed range of heavy-duty engines. Moreover, due to the slower motion of the needle, closing lasts longer in OME operation. The maximum mass flow rate is higher than in diesel operation. A purpose-built 0D-/1D-simulation model of a single-cylinder research engine in OME operation allows an evaluation of different injection strategies: A full-factorial simulation of several operating points shows that the high ignitability of OME enables the omission of pilot injection without disadvantages in NO_x emission or fuel consumption. Furthermore, the maximum pressure gradient of combustion remains approximately the same with and without pilot injection. Therefore, this measure does not provide advantages in acoustics in OME operation. This effect is also due to the lower energy flow gradient, caused by the decreased lower heating value, which reduces the so-called premixed-peak. The results indicate that for a Pareto-optimal operation with OME regarding NO_x emission and fuel consumption around a relative air-fuel ratio of 1.2, high rail pressures are necessary with the EGR rate and the start of injection serving as Pareto control parameters for moving on the Pareto front.