On-Site DME Generation from Methanol for Pilot Injection in CI Engines

Dual fuel (CI) engines provide an excellent means of maintaining high thermal efficiency and power while reducing emissions, particularly in situations where the primary fuel does not exhibit good auto-ignition characteristics. This is especially true of diesel engines operating on natural gas; usually in stationary applications such as distributed power generation. However, because two fuels are needed, the reliability of the engine is compromised. Therefore, this paper describes the first phase of a project that is to eventually manufacture dimethyl ether (DME) from natural gas and supply it to the pilot injector of a dual fuel engine.

A chemical pilot plant has been built and operated, demonstrating an intermediate step in the production of DME from natural gas. DME is manufactured from methanol for pilot injection into a dual fuel engine operating with natural gas as the main fuel. Presently, 0.38 kilogram of DME fuel is produced per kilogram of methanol feed into the process via a catalytic reaction. Future improvements in separation efficiency should improve this to ∼0.53 kg DME / kg methanol feed. The plant is capable of supplying DME of sufficient fuel quality (i.e., DME containing < 10 wt% H₂O and < 10 wt% methanol) to the fuel injection system at a pressure of 15 bar_a and a flow-rate of 1.5-2.0 kg_DME/hr. This would be enough to provide a ½ LHV% pilot of DME to a 1000 bkW dual fuel engine with 42% thermal efficiency. Byproducts of the process situate into two liquid phases, each containing amounts of DME, methanol, and water.