The Interview, Part 1Interviewing a university professor who is expert in combustion behaviour, alternative fuels and the future of the internal combustion engine...By Julian Edgar, pics by Michael KnowlingClick on pics to view larger images | |
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So what is the background of Professor Harry Watson, of the University of Melbourne?
"I built my first reciprocating engine when I was aged between eight and ten and built my first jet engine when I was fifteen. In the period when I was between twelve and fifteen I prepared a motocross motorcycle for one of my friends who was a rider, and got introduced to an off-roading guy called Phil Irving who wrote a book called Tuning For Speed.
"I decided that I ought to go to university to learn more about how to do these things.
"When I was 22 I designed a body for the competition Jaguar D-Type because one of the visiting speakers was a racing driver who couldn't get a car out of Jaguar. So he said 'Would you design one of these - you have just completed your masters degree in aerodynamics, you must be able to do this!' That led to working on the whole of the car. Just before I left the UK I did the complete body design for the Formula 1 Cooper Maserati.
"That was almost 34 years ago - since I moved here [to Australia] I worked for Repco Engine Developments as a consultant then almost continuously I have had some area of interest in developing a better understanding for race car engines as well as looking at the alternative fuel side.
"I did my PhD - into the combustion of hydrogen in engines - at Imperial College in London, particularly looking at the understanding of the knocking phenomenon - this occurs when you have either poor quality fuel or too high a compression ratio. So that was the first attempted to try to understand the chemical processes that lead to knocking. I then went on to do a research fellowship where I looked at an area that is just being revisited, and that is homogeneous compression ignition of fuel/air mixtures - the HCCI engine. There's a partial exhibit available in the marketplace in some of the Honda motorcycle engines which run in that mode.
"Then I came to the University of Melbourne and held various appointments, until in 1996 I was appointed to a personal chair in Mechanical and Manufacturing Engineering."
Alternative Fuels
Professor Watson is in expert in alterative fuels technology, so what better topic to start on? Like, which is the pick of the bunch in alternative fuels such as ethanal, methane, LPG and the others?
"The pick of the bunch depends on what boundary conditions you put on the problem.
"If it's power output, then there are some clear winners - and they are already in the marketplace. They are the fuels that carry around their own oxygen - methanal, nitro and so on. They add extra energy to the combustion process by providing it in liquid fuel, almost in the same way as with explosives. They contain the combustible material and the oxygen that's necessary to make the big bang. That's clearly identifiable technology if you have free [ie no restriction] fuel.
"If you want to worry about sustainability and long term availability of fuels, then plainly fuels like ethanol or methane look to be particularly attractive. It's not always realised that some countries - like China - have well over 100,000 waste digesters that currently produce methane gas. Essentially that gas is used for household cooking and lighting purposes but there are examples we have used for transport as well. That's an opportunity of a renewable fuel to run in competition with ethanol, which we know in this country as coming from sugar cane, cassava and historically other products like sugar beet. It doesn't have to be those sort of plants either - you can use trees, although converting the cellulose is a bit more difficult.
"So that's perhaps the area for the longer term - and historically I might have thought that 'longer term' would have been about now. But we are discovering increasingly more and more oil, and more and more natural gas. So that longer term vision is probably beyond 2050, whereas if you had asked me that same question in 1975 I would have said that it would have been about 1985 or 1990. That's how our perception of the world has changed, and one has to be a bit careful."
CNG
"If we wanted to have a fuel that was high performance, clean, greenhouse gas friendly - in other words, not penalising the environment as much as petrol - then you'd say that would be natural gas. The octane number of natural gas is over 130, so that compares with the highest pump grade fuels that we can buy in this country of 98, which is Shell Optimax or some similar product. Because natural gas is available in the world in quantities of at least twice as much as there is oil, that's an opportunity for the longer term.
"In New Zealand up until recently there was the world's only plant for converting natural gas into petrol. They actually converted natural gas into methanol into petrol. In the oil crisis of the Seventies and early Eighties that plant came on stream and provided the country with half of its petrol through the synthetic route. Elsewhere there are other synthetic fuels being produced - notably Shell's refinery in Singapore that is producing synthetic diesel fuel. So there are these opportunities which are intermediate.
"But if you look at what it costs in energy to produce these fuels, there are some significant penalties - so you'd have to say: 'Why not use the fuel as it is?' The difficulty is that Compressed Natural Gas - even compressed to 700 atmospheres, which is about 3.5 times the allowable pressure that we can have in tanks in this country at this stage - still needs about three times the tank space for an equivalent volume of petrol. That's a bit of a negative, but on the other hand, the energy conversion efficiencies of natural gas - taking advantage of its high octane number - are quite significant. For example, in 1996 we worked with the Ford Motor Company to produce about a dozen natural gas taxies. The engines in the best of those had a maximum efficiency of over 40 per cent, compared with just over 30 per cent for the petrol engine.
"That improvement in efficiency is significant - added to the bonus that natural gas has of having less carbon per unit of energy, it's possible to conceive vehicles that produce 45 per cent less carbon dioxide than a petrol equivalent. The major difficulty from the point of view of the consumer is the distribution [of the fuel] in the marketplace."
LPG
"LPG has taken 30 years to get into the marketplace. At the moment Ford are the only producer of a dedicated fuel LPG car, but it's my understanding that the other [Australian] manufacturers might also soon be producing dedicated LPG-fuelled vehicles. Australia is probably uniquely placed worldwide in being able to put dedicated fuelled vehicles into the marketplace because nearly 40 per cent of service stations around the country will supply you with LP gas. My guess is that the number of service stations that supply diesel fuel is probably about 60 per cent so [LPG] has moved into being a readily available fuel.
"LPG performs just as well as petrol. It plainly is a much lower cost product and I know from the work that we've done on air pollution that it typically is cleaner - perhaps only just cleaner than petrol, because the LPG technology has not advanced to the same extent as petrol engine technology - and it certainly is more environmentally friendly. We did a study a couple of years ago that showed that it was producing 11 per cent less carbon dioxide than a petrol-equivalent vehicle.
"Some downsides [of LPG] are you need to have surety of range - the car I have will go 1000 kilometres between refills on the highway - but you are carrying 115 litres of fuel in the boot and that means that the spare wheel has to be displaced."
Hydrogen
"Most manufacturers looking at hydrogen are looking at it not for combustion engines, but for fuel cells. These take in the hydrogen and convert it directly to electric energy. The technology is not uncomplicated, although the potential efficiencies are high for the fuel cell - like 70 per cent. The best of our current hydrogen [fuelled internal combustion] engines are probably half that.
"So you would say that the fuel cell looks very promising.
"However, there are lots of issues about that which relate to the amount of energy that you need to supply to provide air and other things to the fuel cells - and also, how you provide the hydrogen itself. If you use natural gas - which would probably be the preferred fuel [over hydrogen] - you then have the storage issues that we have talked about. You [also] have to have an on-board chemical works that takes the natural gas and converts it to hydrogen - that's called a 'reformer'.
"That reforming technology may be the key to lifting hydrogen internal combustion engines' performance. In our lab we have recently been looking at that, perhaps prompted by a visit from BMW a couple of years ago. For the last decade we have been developing an ignition process that uses a very small amount of hydrogen to burn conventional fuels with a much greater efficiency. BMW's visit prompted us to see what would happen if we applied a hydrogen-assisted ignition to a hydrogen fuel engine.
"It sounds a bit illogical but the concept behind that is that there is a little ignition chamber - called a 'pre-chamber' - built above the sparkplug. In volume it is about the size of your little finger's length up to the root of the finger nail. It has a very small amount of hydrogen going in there which when ignited, provides partially burned hydrogen products and other chemicals that make the fuel in the main chamber of the engine burn much faster.
"So we're actually able to run very, very lean hydrogen main chamber mixtures ignited by this accelerated process. That means that we can burn mixtures quite successfully up to 3.5 times the normal air/fuel ratio. Lots of excess air [is used] which gives very little throttling, reducing the pumping losses. The amount of fuel that you are using is similar to that which you would be using if you were driving normally around town, with a quarter throttle or something of that sort. [But] what you are doing here is filling the chamber with extra air, so that you are actually using nearly full throttle but you are burning this very lean mixture. If you want extra power, then you achieve that by putting in more fuel.
"The result is an increase in efficiency to about 43 or 44 per cent from a base of 35 per cent, and no emissions of oxides of nitrogen.
"With a hydrogen-fuelled engine you have a ready supply of this small amount of hydrogen for the pre-combustion chamber. With a conventional fuel you need some reforming process to provide this hydrogen. A fuel cell needs 99.99 per cent pure hydrogen but [a pre-combustion chamber] requires only 70 per cent pure hydrogen.
"The hydrogen pre-combustion process is suitable for engines fuelled by methane, natural gas, alcohol... Some of the efficiency improvements are there too - our latest engine work with direct-injected natural gas enabled us to get thermal efficiencies of 45 per cent. That's with natural gas - easy to reform to hydrogen for the pre-combustion chamber."
The Interview, Part 2Interviewing a university professor who is expert in combustion behaviour, alternative fuels and the future of the internal combustion engine...By Julian Edgar, pics by Michael KnowlingClick on pics to view larger images | |
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Last week when we talked to Professor Harry Watson we concentrated on alternative fuels, which with the exception of LPG, it's fair to say are still a long way off from being widely adopted. This week we look at the development potential left in the petrol-fuelled internal combustion engine - are there big gains still possible with this technology? And what about water injection and oxygen enrichment technologies?
Firstly, Professor Watson is a fan of turbocharging.
"We had a turbocharger project with Holden in the middle Eighties for the 2-litre Camira. We took their 1.3-litre Opel engine and turbocharged it for fuel efficiency. We did a lot to manifold design, camshaft design, combustion chamber design and so on. It had identical power output and torque to the Camira engine but under steady-state driving conditions the turbo engine was 40 per cent more fuel-efficient than the larger 2-litre engine. In around-town driving conditions it was about 20 per cent better."
Professor Watson also believes that direct injection - where the fuel is injected into the combustion chamber under high pressure - has potential.
"Gasoline direct injection - or stratified charge spark ignition engines - which Mitsubishi has been producing for the Japanese and European markets now for five or six years has the potential to deliver [efficiency] improvements. There are, however, some issues.
"Much of the testing originally done for the Japanese market was over their rather lemon-type drive cycle, where you have to have an average speed of 15 km/h. You get these [efficiency] gains under those circumstances but when you have a need for higher acceleration - which we're expecting - then there may be some loss from the claimed 18 per cent gains back to about 10 per cent. But that's certainly a big opportunity."
But it's in the optimisation of existing technologies where Professor Watson sees the biggest potentials for efficiency gains.
"One of the interesting studies that we have been doing in our research work over the last three or four years is to develop [engine] optimising technologies. These are based on computer models of the engine. We've taken a range of optimising techniques, starting with neural networks - which are used quite a lot in some areas of optimisation in manufacturing processes - and now we have a method called 'swarm particle tracking'.
"For the current Ford Falcon engine we have 12 variables [in the model] which can all be simultaneously changed within limits which have been calibrated. For example, compression ratio (typically we put the limit at 16:1 on compression ratio), timing changes, the ability to model cam timing, cam phasing, cam duration, combustion chamber shape, engine speed. So there's a whole list of variables, including more obscure things like exhaust gas recirculation.
"What we're finding through this modelling work is that gains of much more than 10 per cent are possible. I think that this bodes well for significant improvements in efficiency that are going to come from optimisation of the engine. Firstly, perhaps before the engine goes into production.
"But the latest stage is real-time self-optimisation with learning strategies. Our ultimate vision for the long-term future is an engine which effectively is put together with some of the mechanical things having limitations but thereafter it will search for its own operating conditions to meet particular requirements of emissions standards and so on. That's a very long-term vision; probably a 30-year work program.
"This technology is particularly applicable when we have hydrogen-assisted ignition process where we can alter combustion duration - an extra variable, something that you can't normally control.
"What we have seen is that the numbers that come out of a simulation for the present Falcon engine show that the cam phasing is very close to what they actually use. But quite surprisingly, as you increase the power output, it seems to indicate that you go to other strategies of cam phasing which are not presently in the Falcon. So in fact instead of running very late inlet valve closing, run it very early. That way you actually trap more of the residual gas from the previous cycle and you get the same reduction in pumping work but now you get some extra stuff in there to help the emissions side of the equation.
"If we think of what's happened to the computer over the last 20 years, then it's obviously only a matter of time before such sophistication [of optimisation] can exist."
One of the other areas we asked Professor Watson about was technologies that have proved very strong in the past but are now currently out of fashion in high performance applications. What sort of technologies, then? Try water injection.
"The proof of the technology is that when performance was of paramount importance in [World War II] fighter aircraft, it was employed - and quite successfully. What it effectively does is reduce the combustion charge temperature through the evaporation of the water. We know that's one way of avoiding detonation; we know that's one way of getting more charge into the combustion chamber to get more power out of the engine. That side of it stacks up very well.
"How you evaporate the water is quite critical - getting a good break-up of the water spray in order that it vaporises very quickly. That's as much of an issue as it is for delivering petrol through a petrol injector, except - and if I can use the word - the 'evaporability' of the water is not as good as that of petrol.
"But the major issue for long-term use of water injection is that the water tends to find its way into the lubricating oil and you have diluted lubricant. In fact in my experience, engines where the lube oil suddenly starts to run out of the filler because there's so much water contamination! So unless it is well managed and there are some cycles that boil the water out of the oil, there are some problems that lead to bearing failure and corrosion. I think that is probably the reason that it is not being played with on any performance applications.
"But I put to you that with the continuing development of metallurgy and possibility of having better sensors, cycling the lube oil, controlling temperature and so on, that water injection is an area that could reasonably be revisited.
"I might just add that in one of our hydrogen cars where we needed water injection for other reasons - that being to keep the combustion chamber surfaces cool to prevent the hydrogen self-igniting - we found that a dribble feed water injection system was the best outcome, quite different from the one that we're talking about here.
"We put an exhaust T-piece [on that car] so that some of the exhaust passed through a condenser, [allowing us] to condense the water from the exhaust. There might not be any need to have a water refuelling process as part of water injection. The concept of this is that it is a built-in system that works without the driver realising that he has the benefit of such technology.
"Even ordinary [petrol engine] exhaust has got 8 per cent water!"
Another 'combustion enhancer' is the boosting of the oxygen content of the combustion air, recently covered in an AutoSpeed story ["The Latest in Intakes"]. The Caterpillar company has a patent on one version of the process, using semi-permeable membranes. Professor Watson has also worked in this area.
"We hold a patent that covers the application of semi-permeable membranes and turbochargers to any sort of engine. The benefits of using these membranes is that you can produce on board the vehicle oxygen-enriched streams. On our demonstration engine we achieved 35 per cent oxygen compared to the normal 21 per cent in air. That [configuration] used twin turbos in a V8 to provide that level of oxygen. That was a diesel engine but we have also done work with a spark-ignition engine equivalent, but not in an engine where it provided its own oxygen.
"There are some significant benefits in both engines of using this type of technology. If you are using turbocharging you have to push nitrogen and oxygen into the cylinder in the usual proportions [contained within air] in order to get the oxygen. If you just push in extra oxygen - which is possible by this means - then the compression pressures and temperatures throughout the engine cycle are reduced. This means where you have a stationary diesel engine producing maybe 16 megawatts you can actually reduce the exhaust temperature considerably for the same amount of output, or you can push up your output for the same exhaust temperature.
"There has to be a downside, and that is that the extra oxygen combines more readily with the nitrogen that remains and so you get increased oxides of nitrogen [emissions]. In order to sell this into a market that's getting ever more keen about oxides of nitrogen levels - even for stationary engines - you need to manage the control very well so that you can find a region where you're getting all of the benefits from the oxygen boosting but there's not too much oxygen available so that you get the high oxides of nitrogen. In fact water injection works extraordinarily well in that role - so combining the two technologies is a very possible solution.
"The membrane technology has come on a lot in the last ten years but it would be fair to say that the membrane that we have on our diesel engine is probably about three times the size of the normal airbox of the diesel engine. But the efficiency of these membranes - in terms of the amount of volume that you need for a given amount of oxygen to be produced - has improved quite a lot.
"It is important to recognise that in addition to the turbo and the membrane you need to have an auxiliary fan. You need to make sure that the fibres of the membrane always see fresh air, so you have to be continually drawing air across the front of the membrane. In a high velocity vehicle that might be provided naturally, but at low speed you need to have that additional item."
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