Heating intake charge and/or fuel....?

I was reading an article in this months PPC about an 'interesting engine' that used the heat from the exhaust to warm the intake air charge to about 250ºC. The result was massively improved performance and indeed an increase in fuel efficiency. The rationale for the improvement was much better atomisation of the fuel, and thus improved burn, and a reduction in Hydrocarbon emissions. Now, what I can't understand is why this actually works? Surely you want to cool the charge and get more air in to improve combustion. Following this logic, you'd think that all these people fitting inter-coolers, or cold air feeds etc. are actually doing the opposite to what would give the best results.

Could you combine the two and say, heat the fuel to around 250°C before firing it into the engine, to improve atomisation and then still use a cold air feed or inter-cooler if turbo??

According to Boyle's law, if the intake air is 250 deg C, you would need 66% less fuel than you would at 20 deg C, which is why it's so economical.

How it makes so much power with so little fuel I'm not sure, although less fuel does burn a lot faster, which potentially pushes the pistons down faster and harder?

Another interesting debate

I haven't read that particular "Weird engines of the world" peice yet but one of the headlines that caught my eye was, "if it worked, it would make XXXhp and do 60mpg"

I think the "if it worked...." bit is telling Stu

Did you see last month's weird engine? A jet engine in a Rover? LOL!

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Doesn't increasing fuel pressure improve atomisation? Would you achieve better results using 5bar fuel pressure and smaller injectors than 3bar and larger injectors?

More pressure can indeed improve atomisation, although sometimes it's counter productive. Some injectors physically don't pass fuel at certain pressures, 70psi in the case of the Delphi / Rochester ball-n-socket injector.

70psi may sound a lot, but if you're running 4 bar static rail pressure (60psi) to get a good idle with large injectors, that only leaves 10psi of boost before the injectors shut down!!

This is partly why a lot of OE turbo engines run 3 bar static pressure (i.e. at atmospheric pressure) so that they don't exceed 5 bar on boost.

You can of course run high pressure if the fuel system is up to it and you can get great results!

Ok maybe I'm being a bit thick here, but on say an OE fuel system on a turbo application. does the fuel pressure rise with the RPM? I would think not given you can get rising rate regs...

It varies with the manifold pressure, I assume. Like on N/A cars.

OEs use a 1:1 fuel reg mate and yep, the pressure rises with manifold pressure.

If you have, say, a 4 bar reg fitted, at idle you will usually see ~ 2.5 bar, at wide open throttle you'll see 4 bar and with 1 bar boost, you'll get 5 bar pressure.

That's why they're known as 1:1 regs, because fuel pressure is directly proportional to manifold (absolute) pressure.

Rising rate regulators are usually 2:1 or often a lot higher. The Begi for example can rise up to 10:1!

I have a digitial fuel pressure guage in the car so that I can check that fuel pressure matches boost pressure. It's a good way of seeing if the fuel pumps are keeping up and / or dying.

EDIT: - Toad beat me to it

kevhaywire wrote:More pressure can indeed improve atomisation, although sometimes it's counter productive. Some injectors physically don't pass fuel at certain pressures, 70psi in the case of the Delphi / Rochester ball-n-socket injector.

70psi may sound a lot, but if you're running 4 bar static rail pressure (60psi) to get a good idle with large injectors, that only leaves 10psi of boost before the injectors shut down!!

This is partly why a lot of OE turbo engines run 3 bar static pressure (i.e. at atmospheric pressure) so that they don't exceed 5 bar on boost.

You can of course run high pressure if the fuel system is up to it and you can get great results!

Would using two sets of smaller injectors then be able to support this? I.e. if you can get better atomisation with higher pressures, using two sets of smaller injectors at higher pressures would give enough 'room' in their operating range...

I had a friend who directed his (petrol engine's) air intake at a hot area in the engine bay, rather than the manufacturer's standard cool air-feed. He reported an increase in MPG. One theoretical reason he gave for this improvement was that with less dense air, the throttle will be opened wider to supply the appropriate amount of oxygen, meaning that the pumping losses in the engine are reduced, (i.e., the engine does less work to suck the intake air past a throttle that is more open).

It sounded reasonable that in a steady-state, i.e, a 50mph commute on the A10, and in closed-loop mode that the engine's pumping losses would be reduced and hence economy would be improved. I'm sure that other factors mentioned above could also come into play. Obviously his experiment wasn't doing anything like 250C air charge temps though and his aims were improved economy and not power.

Anyone who's driven anything will have noticed a big drop in torque on a hot summer's day which makes me a bit cynical about this theory. I'm sure that any power gain must be reliant on some clever new multi-injection strategy or something.