The research for sustainable alternative fuels for combustion engines was driven by the urgency to meet future emission regulation norms and mitigate climate change and dependency on fossil fuels. In this context, methanol emerges as a promising candidate due to its potential for greenhouse gas-neutral production methods and its advantageous characteristics for employment in SI engines. Adverse effects, such as elevated emissions due to incomplete combustion along with liner impingement and oil dilution as a consequence of the high injected fuel mass and the large enthalpy of vaporization, can be improved by a dual injection concept.
The tests were conducted on a single-cylinder research engine derived from a common passenger vehicle engine. The exhaust gas composition was measured with an FTIR-analyzer employing a methanol-specific evaluation method, standard exhaust gas analyzers, and a solid particle counter system with 10 and 23 μm cut-off sizes. The ratio of DI mass to total mass injected in one cycle (xDI) was varied at low-, mid-, and high-load operation points at 2000 rpm and stoichiometric conditions. Further investigations for lean-burn concepts with a variation of xDI were carried out and evaluated based on variables such as engine performance, efficiency, and emissions.
The measurements show a strong charge cooling effect for DI, thereby reducing NOx, although this effect saturates at a mid-load. By splitting the injected fuel mass, an xDI of 30 % shows the highest reduction in NOx at high-load and a reduction of unburned fuel in the exhaust gas of up to 62 %. Particle measurements indicate the interaction of methanol with the liner for both PFI and DI, leading to increased particle emissions. For high-load and dual injection with xDI = 30 % and 50 %, these emissions are found on a level one magnitude lower than compared to DI operation. Lean burn operation with dual injection shows the extension of the lean burn limit at certain points. However, the potential efficiency increase is diminished by undesirable combustion characteristics with prolonged burn durations.