DRIVING THE DUAL-FUEL CAT
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CM has had an exclusive drive in one of ERF's Cat-powered dual-fuel development tractive units.
The first thing you notice about the 4x2 EC12 tractor is its enormous shiny gas tank, which holds 464 litres of LNG. A layer of frost around the filler pipe highlights the fact that the gas is frozen into a liquid before it's pumped under pressure into the tank. On t le other side of the tractor's chassis is a conventional 160-litre diesel tank. Firing up the 12-litre Cat engine requires nothing more than a twist of the ignition key Diesel is fed into the cylinders when idling and the Cat ticks over like any ordinary engine. However, as you pull away and demand more power LNG is progressively fed into each cylinder (see main text), with the igniting gas creating a noticeable rapid rumble, rather like an exhaust brake or a misfire. This process is also accompanied by a brief but noticeable judder through the steering wheel.
Once all the cylinders are running on LNG the environmental benefits soon become apparent. There's no exhaust to see and when driving along the motorway the vehicle is impressivelyquiet.
In general the dualfuel C12, rated at 330hp, is a little more peaky when fuelled with LNG—unlike a normal diesel engine, it doesn't like lugging down below 1,000rpm. When we let the revs on our fully laden artc drop to below 1,000rpm before pressing our foot back flat on the throttle, the Cat engine's ECM seemed to be confused, applying power on a full orVoff basis and creating an unpleasant bouncing motion in the cab. To overcome this we shifted down a cog and got the revs up to smooth things out again.
ERF fully expects Caterpillar to solve the fuel control problem soon, treating a smoother transition from running on LNG back to diesel.
ERF senior devel
opment engineer Andrew Whitehouse says the Sandbachbased truck maker is also likely to get involved in getting the engine's control software sorted out
However, until the Cat engine's glitches are fully removed, ERF will be holding back on final deliveries to customers.