Dual-fuel Cat engine gives ERF the best of both worlds
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• by Brian Weatherley ERF is pushing ahead with the development of its range of alternative-fuelled vehicles to meet the growing demand for environmentally friendly trucks, reports managing director John Bryant.
ERF has already supplied around 75 gaspowered vehicles, including refuse collectors, to LK operators and Bryant says that the company Is planning to sell a further 200 during the next 12 months.
Among the engines currently being evaluated by the Sandbach-based truck maker is Caterpillar's 12-litre, dual-fuel diesel/gas C12, which will be offered in rigids and tractors. The in-line six-cylinder dual-fuel C12 engine uses diesel as the ignition medium, keeping its normal compression ratio, and can run with either compressed or liquefied natural gas (CNG/LNG).
Following the takeover of Perkins by Cat, the C12 has already replaced the Eagle Tx as the American engine company's large displacement alternativefuel engine. However, the unit is not without its teething troubles which have come to light during evaluation trials with the chassis manufacturer (see driving impressions).
The diesel/gas C12 Cat offers clear improvements in emissions and noise over a conventional engine, The
dual-fuel com•'
bination is • • delivered via Servojet Technologies' multi-point, port-injected delivery valves, working with Cat's own electronically controlledcontrolled diesel injection system.
The whole engine is controlled by Cat's Advanced Diesel Engine Management System (ADEM), and Servojet's Eagle ECU.
In normal operation, diesel is used as the initial starting fuel up to 20% engine load. Then, as more power is demanded by the driver, three of the C12's cylinders are switched to LNG then four, and five, before the engine's efficiency increases to the point at which all six cylinders are running on gas. This "skip-fire" process takes place within a few seconds.
The dual-fuel concept gets over the problem of gas-powered vehicles requiring set routes and expensive infrastructure; when LNG is not available the engine reverts to normal diesel operation. And, while it still sounds like a diesel when idling, noise levels and emissions drop correspondingly when it is running on gas.