An experimental study on methanol as a fuel in large bore high speed engine applications - Port fuel injected spark ignited combustion

Experiments were conducted on a single cylinder large bore high speed diesel engine with - 5 l cylinder displacement converted to a port fuel injected (PFI) spark ignited (SI) methanol combustion system. The effects of the relative air/fuel ratio (rel. AFR), back pressure and engine load on the engine performance as well as NOX, CO, HC, methanol and formaldehyde emissions were studied. The major objective was to evaluate if the substantial benefits of methanol on smaller passenger car engines can be conveyed to larger engines as methanol is sensitive to hot surface ignition and preignitions are favored by the long burn distances and hence longer dwell time at high temperatures. The study results show that the significant benefits of methanol regarding engine performance can be reproduced also for large bore high speed engines. Preignitions were not found to be an issue and engine knock was the limiting factor for the engine load achievable. The results show brake thermal efficiencies above state-ofthe-art natural gas engines in the same displacement class (- 44%) for a projected full scope PFI SI engine and indicate potential for further optimization. NOX emission compliance with the International Maritime Organizations (IMO) Tier III limits (<2 g/kWh) can be achieved without exhaust gas aftertreatment. However, regarding unburned methanol and especially formaldehyde (-1 g/kWh), the application of an oxidation catalyst is advisable although not required to fulfill IMO Tier III.