Stoichiometric methanol autoignition and in-cycle knock suppression using direct water injection

Abstract

Methanol as a fuel is gaining popularity due to its favorable properties and potential for sustainable production as bio- or electro-methanol. By operating according to the Spark-Ignited (SI) principle with a Three-Way Catalyst (TWC), low emissions can be achieved. The main phenomena limiting the efficiency of the SI engine when operating with stoichiometric mixtures are knock and, occasionally, pre-ignition. One method to suppress both knock and pre-ignition is water injection. This study explores the possibility of suppressing knock in-cycle using direct water injection for cycles with an elevated risk of knocking. The prediction was based on the observation that, at knock-limited operation, only cycles with the most advanced combustion phasing knock. Furthermore, at knock-limited loads, combustion predominantly consisted of a single combustion mode: deflagration. The results demonstrated partial knock suppression and allowed for a combustion phasing advancement of 1.5°at loads of 10 and 15 bar gross indicated mean effective pressure. The earliest practical point during the combustion cycle to confidently determine if knock will occur was when about 10%–20% of the fuel had been consumed. However, theoretically, in a best-case scenario, this could be as early as when 5% of the fuel was consumed. An experiment simulating pre-ignition also demonstrated the ability to detect such cycles and partially suppress the ensuing knock. A major limitation of the method is that the window between detecting a cycle with a high likelihood of knock and knock onset was less than 7°at 1000 rpm.