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It is substantially politics and local factors that decide fuel directions – rather than medium and long term environmental interests. America, for example derives only 5% of its oil from areas that it currently dislikes. Moving to a 5% ethanol content enables that country to purchase the remaining 20% (of that needed from overseas) from countries it (currently) sees as ‘friendly’.
Australia has a lot of LPG and it makes economic sense to concentrate on that – in fact the present government seeks to have a substantial part of the transport fleet running on LPG by as soon as 2010. In Europe however the trend is to seemingly ever-more efficient turbo-diesels, even for small cars and, hybrids apart, it is probable that Japan will follow this path.
It is likely therefore that a substantial number of buyers of new campervans and motorhomes will end up with a turbo-diesel. And one can do a lot worse than that.
Until quite recently, diesel engines produced a considerable amount of airborne particulates resulting in unacceptable local pollution. This was not due to the engine design as such, but to the high sulphur content in the fuel necessary, amongst other things, to safeguard rubber-based oil seals.
Fortunately those days have all but gone as worldwide, that sulphur content is being reduced effectively to zero. (This is likely to create problems with oil seals in many older engines and if you have not attended to this by now I suggest you talk to a diesel mechanic about it soon.)
The virtual removal of sulphur has eliminated local (particulate) pollution. The sulphur removal process itself generates a small amount of greenhouse emission but this is more than offset by the greater engine efficiency that the clean fuel permits.
The now much cleaner fuel is enabling a still ongoing and virtual revolution in diesel engine development. Already, today’s turbo diesels are quieter and smoother. They produce up to 30% more torque and power from much the same capacity meanwhile also using less fuel. As an example, the just introduced and close to 5 litre V8 turbo diesel in the new Toyota Troopy uses only 80% or so of the fuel of its much less powerful 4.5 litre six-cylinder predecessor. A fair bit of this advance is due to so-called common rail injection.
In a conventional diesel engine, a high pressure distributor pump, controlled by the engine’s perceived needs, injects bursts of fuel into injectors. It’s a somewhat crude system but it’s very reliable and has worked well for many decades.
The so-called common rail system was devised about ten years ago, but only came into general use in 2003 or so with the advent of cleaner diesel fuel. It works by maintaining a small reservoir of diesel fuel (called the rail) that is maintained at the ultra-high pressure at about 1600 bar (that’s about 22,500 psi). The pressurised fuel is then fed directly to computer-controlled injection valves.
These valves may consist of electronically controlled plungers and nozzles driven by solenoids – or piezo electric crystal actuators that change shape when you whack a voltage across them.
In effect, common rail injection ensures the cylinders receive precisely the amount of fuel required and at the precise time it is needed – and it does so across the whole range of engine speeds and loads. The technology reduces pollution by about 20% and can provide a lot more power and significantly lower consumption.
Turbo charging is now pretty much taken for granted with even small diesel engines. Without it, an engine has to generate a fair bit of power simply to suck in the huge amounts of air that is needed for that diesel fuel to burn.
A turbocharger is simply a big air pump that rather than being driven by the engine uses the heat energy otherwise wasted via the exhaust to do the same job. This increases power output and/or efficiency by 10-15%. And if you don’t use that extra power by driving faster or accelerating harder you’ll have a corresponding saving in fuel.
About the only problem with turbo chargers is that as they pump air they heat it up. (You can experience this effect when you use a bicycle pump). Whilst this can be handy, not least because it’s how a diesel engine works, it has the downside that when air is heated it becomes less dense: in effect there is less of it. As a direct consequence, some of the turbo-charger’s benefit is lost.
To overcome this it is increasingly common to fit an intercooler. This is simply a strong radiator fitted between the turbocharger and the engine that cools the pumped air. This regains that lost few per cent efficiency (5% is typical).
Intercoolers can be retrofitted, but at a typical $1500 plus, one needs to have a look at cost versus savings.
If you inject a diesel engine with discrete amounts of LPG you get an appreciable increase in power and an overall saving in fuel. This is actually a very old technique that truckies have been doing for decades: they simply use a big LPG cylinder, a basic control valve in the driving cab, and inject the gas into the engine’s air intake manifold. It works very well but at not inconsiderable risk of overheating, and even blowing the engine apart if the gas valve is opened too wide.
The technique has recently been made safer and more reliable by using computer controlled LPG injection. There are several companies around specialising in this field. The normal ratio is two parts of diesel to one part of LPG and this results in claimed increases in power of up to 20%, and reductions in overall consumption (in dollar terms) of at least 10%.
The engine still runs fine on straight diesel – although any benefit is not then gained. The downside is that you need to fill two tanks – each with a different fuel from a different pump. In some towns you may need to go to two separate service stations.
Probably typified by the Toyota Prius, a hybrid typically has a small petrol or diesel engine that provides sufficient power to propel it at a constant speed along a flattish road. An electric motor powered by a battery bank cuts in for accelerating and hill climbing. Energy is saved by using that normally wasted as heat whilst braking by using the electric propulsion motor as a generator.
There are currently about a dozen various hybrid vehicles, but whilst technically interesting, their fuel consumption is much on a par with a few of the more fuel efficient turbo-diesel cars (particularly the small Peugeots). Work is also proceeding on hybrid-engined trucks.
In this field, serious developments still await a major advance in battery technology – and I recollect writing almost those same words in my magazine Electronics Today International back in 1972. Solar is often touted as an energy source for recharging but that seems to overlook that cars are mostly driven during the day.
A conventional petrol engine can be easily adapted to run on hydrogen. BMW has recently produced a small fleet of cars that do just that. Hydrogen is readily produced by any number of ways including passing an electric current through water (this was the true energy source for the ‘water-powered cars’ of a few decades ago).
The problem lies in storing and transporting the stuff although a lot of work is underway to produce it only on demand as required. This is currently being done by using fuels (including LPG) to produce hydrogen, which in turn powers a large fuel cell that in turn drives one or more electric motors. This is far from just theoretical: Perth had several big LPG/hydrogen powered city buses on long-term trial throughout 2006. Whilst complex, this approach has the advantage that fuel cells can be energised from a wide range of fuels, that the process is quiet, and that the energy otherwise lost in braking can be captured and stored – a huge saving in large city vehicles like buses.
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