AT THE HEART OF THE ROAD TRANSPORT INDUSTRY.

Call our Sales Team on 0208 912 2120

n1= ant ROADTEST: LEYLAND DAF FA4511501AFS DUAL-FUEL

19th November 1998
Page 34
Page 36
Page 38
Page 37
Page 34, 19th November 1998 — n1= ant ROADTEST: LEYLAND DAF FA4511501AFS DUAL-FUEL
Close
Noticed an error?
If you've noticed an error in this article please click here to report it so we can fix it.

Which of the following most accurately describes the problem?

CM has evaluated a number of dual-fuel trucks, but this is our first time behind the wheel of a wagon that combines diesel and CNG automatically, to suit operating conditions. The well-used Leyland Daf 7.5 tonner used as a testbed convinced us that this technology has now come of age.

This test is unusual in that the featured truck is not the subject of the test, it's merely the basis for an engine conversion. However, the bonus is a mini used-truck report of a well-used four-year-old Leyland Daf 45. It's a former Exel Logistics vehicle, with a curtainsider body and aero kit on a four-metre wheelbase chassis, powered by a 150hp Cummins B-Series engine, although the conversion is suitable for almost any non-electronically controlled diesel engine.

The conversion in question allows the Cummins engine to run as a true dual-fueldieseland compressed natural gas (CNG)— z

8 simultaneously. Some other systems known g as dual-fuel should strictly be called bi-fuel as 1 they only use one of two fuels independently ,.., t., at any given time.

' So why should anyone want to convert? ..

I Consider a local authority with a sizeable 8 fleet powered by pre-Euro-2 engines, probably with longer-than-average planned lives E. budgeted for. At some point, such an opera

tor is likely to come under pressure to achieve significant reductions in the overall emissions of its fleet.

A conversion such as this one offers the operator a route to achieving this without replacing the existing engine, let alone the whole truck.

The AFS Diesel Dual-Fuel (DDF) system tested is marketed in the UK by Clean Exhaust Emissions Ltd (CEEL) of Luton, but the system downstream of the pressure regulator is made in Canada by the Alternative Fuel Systems Group, the regulator and storage tanks being sourced locally. Although new to the UK, the system has established its credentials world-wide, and is approved as a line-fit option by Caterpillar, Hino, Isuzu and Daewoo.

• PRODUCT PROFILE The basic principle of the system is to mix diesel with CNG in a ratio which varies continuously depending on a number of Olb• 44 conditions. The system's "brains" are provided by an Electronic Engine Control Unit which monitors engine coolant and intake air temperatures, injection pump lever and "drive-by-wire" accelerator pedal positions and crankshaft speed and angle. It then uses the data collected to control the fuel delivery in two ways, having calculated the optimum fuel mix.

Theoretically, the maximum ratio is around 94% CNG, but in practice it's kept to between 70% and 80%. The reason for a certain amount of diesel to be injected at all times is to provide an ignition pilot, as gas alone will not ignite under the amount of compression practical in an engine. This is why other CNG engines use the spark-ignited Otto cycle.

The first part of the fuel-delivery system controls the quantity of diesel injected. This is done by means of an electronically controlled linear actuator attached directly to the injector pump operating lever. The second part of the equation is the gas delivery system. Gas is fed at a precisely regulated 10bar pressure to a bank of high-speed solenoid valves, one per cylinder, mounted to a thin plate sandwiched between the cylinder head and the inlet manifold. The actual manifold design depends on the base engine. As this part of the fuel is by definition a gas, the valves have no high-pressure mixing function but simply deliver the precise quantity of fuel determined by the time they are open. The low pressure, in a relatively cool part of the engine, means the gas can be delivered close to the back of the inlet valve by a length of plain Teflon tubing.

The only part of the hardware not described so far is the tankage, which varies according to application and operator requirements. Tanks can be steel or composite plastic, with the operator choosing an appropriate compromise between cost, payload penalty and range.

A typical installation would consist of three 90-litre steel tanks which, with the associated framework, would weigh in the region of 200kg. But whatever configuration is used, the tank design and installation is governed by strict international safety standards, so worries about exploding tanks can be dispelled.

CEEL's demonstrator is fitted with more tanks than normal, partly to allow accurate consumption testing, but also to overcome the biggest current drawback of alternative fuels—the patchy nature of the fuel-supply infrastructure. It's still struggling to escape from a classic, and well documented, "chicken and egg" situation. Fortunately, if the gas does run out, the system has the facility to run on diesel only, either manually—by flicking a switch in the cab—or automatically; by means of a pressure switch on the gas supply side.

For operators with vehicles returning to base each day there is another option. The Fuel Maker is a low-cost compressor which taps into the domestic natural gas system, providing a compressed supply overnight suitable for vehicle use It can be rented for around £50 per month. With dual-fuel selected start-up is completely normal as the system won't allow gas in until a degree of warming up has been achieved. Apart from keeping the tank filled, there is no requirement for any additional driver input at all.

Sitting at the wheel during dual-fuel running, the conversion is frankly a disappointment, but only because it feels little different to running on diesel alone. True, the stopwatch shows dual-fuel to be somewhat slower than diesel, but when driving, although the difference is noticeable, it certainly doesn't feel as great as the figures suggest. The only other obvious penalty is that slightly more revs are needed to move off, but CEEL reckons this can be improved with a little more tweaking of the computer's fuel map. On the positive side, dual-fuel is noticeably quieter and smoother.

The real gains are shown at the pumps and out of the exhaust pipe. The difficulty in reaching a comparable fuel consumption figure for a vehicle using two fuels is deciding what basis you use for comparison. In this case, we have added the overall costs of both fuels for the trip and converted them back into a figure based on the pump price of diesel.

On this basis, the overall figure was the equivalent of 16.2mpg (17.41it/100km). This figure should be read with due regard to the Dal's 4.08:1 urban diff ratio and to the atrocious weather conditions prevailing during the test. There's no doubt that any real operator could obtain better results.

However, the purpose of this test was not to make straight comparisons with diesel; it was to establish that the principles behind the conversion are sound.

The overall diesel/gas ratio over the test was 66.5% gas. Ironically, the harsher the operating conditions, the more effective the system becomes, as the diesel replacement figure is greater the harder the engine is working—the gas figure in high winds on the motorway section was 85.8%.

As the table below shows, the testbed emissions figures obtained by CEEL indicate that the conversion fitted to a Euro-1 engine in most cases exceeds the anticipated requirements of the forthcoming Euro-3 standard. The main difference at the moment is the total hydrocarbon level (THC), which is not separated into methane and non-methane figures, and therefore appears to be much higher as a result of the increased methane in CNG.

CEEL is currently in the final stages of developing a reverse-flow catalytic converter to reduce all hydrocarbon emissions greatly. Official ''real-world cycle" figures are currently being gathered; we will publish these when they are available.

• THE TRUCK

The test also provided an opportunity to see how a Leyland Daf 45 fared after four years and 300,000km of front-line distribution work. To be honest, this prospect was approached with some trepidation. But in the event the expected dog turned out to be a tribute both to the durability of the original package and to Exel's maintenance standards.

A thorough look around the cab interior revealed nothing more serious than the glue holding the driver's A-pillar trim letting go. The seats were still clean and in good condition and, apart from a little slop in the indicator stalk, all the controls worked as intended. A quick valeting session could have had the whole thing looking showroom fresh, the only sign of its vintage being the rather dated and over-styled instrument panel. On the move our immediate impression was how tight it still felt, with the steering as crisp as new and the handling good enough for the wagon to be driven as quickly as prudence permitted. The most impressive detail was the quality of the gearchange, with perfect synchromesh and absolutely no slop, the ZF box giving away its age only by the amount of chatter at low revs.

The driving experience was marred only by the brake pedal location, which is much too close to the steering column. The airover-hydraulic brakes themselves, although needing fairly firm pressure, were both strong and progressive.

The engine, changed to provide CEEI. with a known benchmark for the conversion, was a Cummins factory reconditioned unit, and reinforced the nearly new feel.

• SUMMARY CEEL's demonstrator shows that the AFS dual-fuel system is a workable and well-engineered solution to a problem. How big that problem is, and hence how much demand there will be for this system, remains to be seen. Much will depend on the cost of the conversion and on how the final official emissions figures place it within the Powershift initiative's grant structure (CM6-12 Nov).

If the estimated cost of £9,500, based on a six-cylinder engine with three 90-litre tanks, could be reduced by the 75% that goes with Powershift's Band 3, then the dual-fuel conversion would be financially realistic for a number of operators.

by Colin Barnett Cost of conversion: £9,500 (typical cost; see text). Engine: 5.9 litres, 145hp (108kW). GVW: 7,490kg. Speed: 63.6km/h. Fuel consumption (laden): 16.2mpg (17.414/100km).

SPECIFICATION

cam Leyland Do) FA45.1 50 dual-fuel

Design GVW: 7,490kg.

Converter: Clean Exhaust Emissions Lid (CEEL), 65 Castle Street, Luton, Beds LU1 3AG (teI: 01582 734353).

IMBEIZEll Cummins B-Series (Leyland Da) CB108) four stroke, direct-injection, charge-cooled turbo-diesel with

AFS CNG conversion.

Cylinders: Six, vertical in-line_

Bore/stroke: 102x120mm.

Capacity: 59 litres.

Compression ratio: 17.0:1 Maximum net power': 108kW (145hp) at 2,600rpm.

Maximum net torque': 350Ibfi (475Nm) at 1,600rpm. (*ISO 1585, running on diesel).

Zf 55-42 five-speed synchromesh gearbox with Leyland Di) SR5/ 12 single-reduction rear axle. Final drive: 4.08:1.

Clutch: Single dry plate 330mm-diameter, air assisted hydraulic. TRANSMISSION: BRAKING SYSTEMS, Dud-circuit, air-over-hydraulic, with spring actuator park brake.

Brake dimensions: Front discs, 315x25mm; rear drums, 325,l 10mm.

EM(til ZF 8090 hydraulic power assisted. Ratio: 15.2.1. Ladder-type high-tensile steel frame with riveted and bolted construction..

Suipension: Parabolic leaf springs with double-acting shock absorbers and anti-roll bars front and rear.

Axle design weights: Front 2.90 tonnes; rear, 4.58 tOlneS. Design 01W: 10.99 tonnes.

Wheels end tyres: 5.25x17.5 six-stud steel wheels with 205/75R 17_5 tyres.

Fuel tank 'typical): Diesel. 123 litres; CNG, 270 litres. CHASSIS

ELECTRICAL SYSTEMS24V earth-return system. Battery: 2x110Ah.

Generator 30A alternator

OPERATIONAL TRIAL RESULTS

Welsh test route: 367.2km (118,2km motorway/249.0km A-road).

Overall: Average speed, 63.6km/h (39.5mph); fuel consumption, 16.2mpg (1 7.41it/1 00km).

Motorway: Average speed, 79.8 km/h (49.6mph); fuel consumption, 18.8mpg 115.0kt/100km).

A-road: Average speed, 57.9 km/h (36.0mph); fuel consumption, 15.2mpg (1 8.61i1/1 00km).

BRAKE PERFORMANCE

Full brake test could not be carried out due to track conditions.

Park brake held on a 33% (1-in-3) gradient facing up and downhill.

TURNING CIRCLE

Between kerbs. 2.8m

HILL PERFORMANCE

Hill min sec

Monmouth bypass 2 32 Wantage 2 46 Restart not possible on 25% (1-in-4) gradient.

WEIGHTS

Kerbweight (with 75kg driver) 3,990kg Net payload* 3,500kg

Total 7,490kg

'Typical payload, dependent on tank capacity.


comments powered by Disqus