Methanol mixing controlled combustion process enabled by onboard methanol dehydration to dimethyl ether (DME)

This work demonstrates an initial proof-of-concept approach for operating a compression ignition off-road and marine relevant engine using neat methanol. The approach utilizes mixing controlled compression ignition (MCCI) of methanol that is enabled by a homogeneous charge compression ignition (HCCI) pre-burn of mostly premixed DME. Although two fuels are used, this work explores and evaluates the opportunity and performance to generate the premixed fuel via methanol catalytic dehydration over an alumina catalyst at engine relevant temperatures, pressures, and space velocities. Detailed bench flow reactor studies of the catalytic dehydration species output and conversion purity results are then coupled with single-cylinder experiments of both the characterized output species for pre-burn HCCI performance. Subsequent initial methanol MCCI performance is also evaluated and compared relative to conventional diesel combustion. The detailed flow reactor results show that the catalytic dehydration conversion efficiency of methanol to DME is a function of system pressure, temperature, and space velocity. The engine results demonstrate that the purity of DME does not need to be 100% for successful pre-burn HCCI, and the water formed during the dehydration process does not need to be removed to achieve the desired HCCI event from this pre-burn mixture. Subsequent methanol MCCI combustion results show that the level of methanol slip in the dehydration process affects the pre-burn HCCI phasing, low temperature heat release process, and magnitude of energy released, all of which can dictate the available window for subsequent methanol injection.