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Isuzu comes clean with dual fuel

17th August 2000, Page 15
17th August 2000
Page 15
Page 15, 17th August 2000 — Isuzu comes clean with dual fuel
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• by Kevin Swallow Isuzu is the latest truck manufacturer to put its faith in gas. Conversion firm Clean Exhaust Emissions (CEEL) has retrofitted a compressed natural gas (CNG) dual fuel system to one of its trucks which is being used by various local authorities as a demonstrator.

Larger truck manufacturers established in the UK have generally steered clear of the dual fuel race. But Isuzu is targeting local authorities and public utility markets, looking to capitalise on councils wanting to appear green by using "cleaner" fuels.

Low-down

CM got the low-down on the retrofitted Diesel/Gas Dual Fuel (DDF) system running on CNG by driving an lsuzu NQR 7.5tonne tipper laden with three tonnes of sand.

The first thing you notice is the size of the diesel tank— reduced from 100 litres to 75 litres. This allows the snug fitting of two 90-litre gas cylinders, one on either side. Apart from that it looks like a regular Isuzu 7.5-tonne tipper truck.

A dedicated gas-only engine uses spark ignition, and needs the paraphernalia of spark plugs, leads, coils and a distributor. The retro Diesel/gas Dual Fuel system can be much simpler, using a conventional compression-ignition system to ignite the diesel fuel, which in turn acts as a "pilot fuel" to start the combustion of the gas.

Under the cab an electronic Engine Control Unit (ECU) is fitted at the front of the engine. This generates output current pulses to gas ieiectors while dictating the position of the diesel pump lever through high-speed solenoid valves. It is unobtrusive and engine maintenance can be done without moving the retrofitting system.

The gas meter is fitted on top of the dash next to the driver's side door-pillar, while there is a green button to engage dual fuel operation, placed by the door at knee height The switch is out of sight so, unless you make a conscious effort to check you have switched it on, you might be run

ning around solely on a reduced diesel tank.

Diesel remains the pilot fuel but CNG replaces 75% of diesel once at optimum speed. From a standing start to 80krn/h the diesel engine slightly eclipsed the dual fuel, but only by a fraction of the 28 seconds the test took to complete—nothing to write home about. The acceleration is smooth and responsive as more of the gas kicks in.

You only realise the difference between driving dual fuel and diesel over longer journeys, when the diesel tank gauge does not drop alarmingly. Travelling along the motorway will produce efficient results using predominantly gas, but these benefits are lost when trekking through city centres mainly on diesel.

Well planned

With only 12 public CNG fuel stations across the country any long gas-only journey has to be very well planned, but the diesel option makes travelling much more flexible.

However, the municipal market should be able to make better use of gas.

The noise of the dual fuel system is noticeably quieter at 71.0dB(A) than the diesel-only engine, measured at 82.0dB(A) at 40mph.

The manufacturer says that it is the only UK company building the retro-fit CNG dual fuel system for commercial vehicles. The advantages are as clear as gas itself: fuel price, reduced emissions, and fuel economy. CNG dual fuel is proving popular with local authorities wanting to appear green and accountable to ratepayers.

The DDF system costs 210,000 (ex-VAT) to fit.

IN Contact 01525 217782.

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Organisations: Engine Control Unit
People: Kevin Swallow

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