Fuel costs will be cut
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Alternative fuels with pilot diesel injection are on the way, says Bradford-born Bill Crampton, who is now technical editor of Canada's Motor Truck magazine REATER dissimilarities may odst than those between the )ft green fields of Derbyshire, le frozen peaks of the Canadian ockies and the arid dryness of exas, but these will do until Dmething better comes up. hey are linked in an event that likely to transform the econolic scenery of all industries movated by that most efficient of Iternal combustion engines — le diesel.
The driving force behind this vent is New Energy Interneanal, Derby and London. In harass with NEI is Anker Gram of ieosource Canada Inc, of Vanouver, British Columbia, while louston, 4,000 miles south rest, houses the Geosource ead office. Geosource is in the usiness of putting together latural gas liquefaction plants; knder Gram is the acknow?Aged authority on LNG in his lailiwick; and Tim Bedford, resident of NEI has a bubblewbble potful of computer cience, alternative energy techiology, and mechanical iardware into which gas and liesel engines can be immersed nd come out smelling sweeter, )roducing more bhp and using ewer British Thermal units of ,omething that did not come out )f an oil well, at least not iecessarily so.
Let me explain. Alternative uels are not new; liquid petroeum gas (LPG or propane, or )utane as used in Italy) and iatural gas (NG-methane) as veil as the alcohols ethanol and nethanol, have been around for rears. But almost without excepion they have been used to funigate the manifolds of petrol ngines.
That most efficient of internal ;ombustion engines, the diesel, las had to be satisfied with the )ccasional use in stationary ap)lications of NG: which meant it as no longer a diesel, the injection system removed and spark Ignition fitted, but at least the application did take some advantage of the 14:1 compression ratio possible with NG.
Natural gas in that kind of use would be readily available from a pipeline, or perhaps virtually free as a product of a landfill site. It would arrive under a few pounds of pressure. In transport use some means has to be found to pack a lot of Btu's in a small space; this usually means in steel cylinders under about 211kgf/sqcm (3,000psi), but sevaral times more energy, at a fraction of the container weight, can be carried on board a truck when the gas is in LNG (liquid natural gas) form.
The trouble with LNG is that it can only be produced at —162°C, which is very cold, even for Canada. However, practical and economic liquefaction is possible and storage tanks exist that can hold LNG for seven to 10 days without boil-off.
The advantage of NG is that it exists in most countries and can in any case be produced from coal. Its disadvantage is that it has a very high ignition temperature of 1,170°F (632°C) as compared for example to 680°F (360°C) for petrol, but a simple solution was identified by Bedford: let pilot injection of diesel serve to light the fire in the cylinder, with fumigated NG providing most of the work performing Btu's. Or LPG can be used in the same way. It works, and it works surprisingly well.
It is known that when LPG is used in a petrol engine there is a great deal less ring and cylinder bore wear, the sump oil stays clean much longer and does not become diluted, spark plugs last much longer and so do exhaust systems, while exhaust emissions are cleaner. (NOx can be high, but most Canadian regulatory agencies appear to be determinedly unaware of the fact.) These benefits should apply to a diesel/NG engine.
There is another benefit, in fact more than one, arising out of a marked change in combustion characteristics when only 10 per cent or so of the fuel is diesel. It shows up in a much quieter engine; gone is the diesel knock. Now the fan and turbocharger become too obvious. But thermal efficiency appears much improved and certainly a considerable gain in horse power is possible. Bedford has taken pains to limit the (lain to about 10 per cent, or enough to avoid the "She don't have the same power" complaint that could be expected from many drivers if output was the same.
Here it maybe useful to note a comment by the head of BC's department of highways (over 9,000 vehicles, including 400 GMC diesel pickup trucks), concerning a Toyota diesel powered pickup that can switch from straight diesel to a 40 per cent diesel/60 per cent CNG at the flick of a switch. "You sure know when she is on the mix," said Tom Yearsly in a decidedly southern English accent, "She just takes off," he explained.
To clear up any confusion, it should be explained there are two types of "dual-fuel" applications: gasoline engines converted to use LPG commonly remain able to switch to petrol should the LPG tank run dry before refuelling is possible. This is even more true of CNG conversions; currently there are only three CNG fuelling stations in Canada: one is in Vancouver, another in Calgary, and a third has just opened in Toronto. CNG-powered vehicles usually are limited to about 80 to 120 miles before the cylinders are exhausted, but, even so, most of the taxi fleets in Vancouver are switching to CNG/gasoline.
Fuel saving amounts to between 40 and 50 per cent. So LPG and CNG, with petrol as a reserve, are both dual-fuel systems.
By contrast, diesel dual fuel means two fuels (CNG or LNG or LPG with diesel) are in use at the same time but here, too, there will almost always be the switch wnich, when thrown, will mean straight diesel use. LPG in diesels, incidentally, is perhaps less attractive as 12:1 is the maximum possible CR possible, compared to the 14:1 for NG.
What has been achieved in Vancouver is the first application of LNG and diesel. It was being installed in a turbocharged Cummins 290 engine, fitted in a White-Freightliner owned by BC Hydro, the province's electircity utility, at the same time that Tom Yearsly was reporting his experience with the Toyota to a meet ing of truck fleet superintendents. (Actually this was the second installation for the kit — the first was in a British truck where the concept was first proven. However, the British truck had a brand new 290 engine; the BC truck is seven years' old, it is showing its age and had a number of faults — such as three different injector types — which had to be corrected.) The age of the hydro truck showed up in a somewhat dirty exhaust which was much cleaner, however, when running on dual fuel; it also produced 230 wheel hp as compared to 210 on diesel. (Conversion to straight diesel is at the flick of a switch.) This conversion of the 290 Cummins is easily described. The truck retains the original fuel tank with the LNG tank on the opposite side being an exact fit for standard mounting brackets. No changes are made to injectors or pump except to mount an arrangement that limits maximum injection to, in this case, 17 per cent of normal. (Combustion and performance would be as good or better on 5 per cent injection, said Bedford, but the injectors would run hot and there would be a risk of spray holes carboning up.) At idle, no LNG is used.
Because LNG is an excellent refrigerant, it is necessary to heat the evaporator with engine coolant. Here it should be borne in mind that a "cold" engine of 32°F is very hot as compared to the —260° of the LNG, but the coolant would need to be well protected with anti-freeze or the evaporator would freeze solid in minutes.
Now comes the problem of phasing in NG in vapour form according to the driver's foot on the pedal and engine rpm. This is accomplished with New Energy International electronics and hardware. Solid-state pressure sensors measure LNG tank pressure, inlet manifold pressure and the PT pump fuel pressure. These signals are fed to an electronic box which reads them to instruct a gas metering unit. There is more, much more, to it than that, but the concept is essentially this simple.
In claiming improved power, improved thermal efficiency, reduced engine noise, less maintenance and longer engine life, the developers explain the first three relate to the very different (to diesel) combustion process which eliminates diesel knock, and the other two to the clean burning (cleaner even than LPG) characteristics of methane.