AEI Show Daily Extras: Monday

Getting heavy with synthetic fuels
In recent years, dimethyl ethyl (DME) has joined the short list of synthetic alternatives for diesel in heavy-duty vehicles. Monday morning during the CI Engine Performance for Use with Alternative Fuels technical session in Room D3-26/27, researchers from Japan's National Traffic Safety and Environment Laboratory and Nissan Diesel Motor discussed their application of a DME engine to a 20-ton (18-t) GVW heavy-duty truck.

DME's high cetane number provides it with nearly the same thermal efficiency as diesel fuel. However, the liquid density of DME is about 80% of diesel fuel, and the specific energy content is about 70% of diesel. Therefore, about twice the DME fuel volume must be injected compared to diesel fuel to ensure the same power output. Also, the compressibility of DME is significantly higher than diesel and it has lower viscosity and lubricity. According to the researchers, all those facts worked together to make it impossible to use a conventional unmodified diesel fuel system for the DME application.

Because of the maximum injection-pressure characteristics of the DME engine, researchers opted for an inline fuel-injection pump with a conventional spring-loaded needle injector. A jerk-pump-type system was chosen because it allows for a relatively low injection pressure at low speeds, while also allowing the injection pressure to increase with increased engine speed.

- Jean L. Broge