Turbocharging with no intercooler, petrol/ethanol
 

So far this is just theoretical, I don't think that I'm going to have budget, time or place to do anything concrete any time in near future, but I'd like to know if I'm after something. There is so much technical knowledge here, that someone got to know or have a relevant argument's at least.

This hypohesis is mainly for ethanol fuel, I think. As we know, ethanol's energy content is lower than petrol. But, because of that it burns a bit cooler. It have a higher octane number too, so it's possible to use higher compression ratios.

So, if a engine running with ethanol is turbocharged with relatively low pressure, let say 7-8psi/0.5bar and no cooling is used, we have a warmer intake air, better fill in cylinder and part of the wasted energy in exhaust gasses is used to produce power, is it going to be better average mpg?

Most of the small modern engines have turbo, but that's maybe mainly to have efficiency benefits of small engine but the power of a bit bigger engine, to make customers happy? But is it possible to charge an engine only to use lesser fuel? Or has it got to be done with longer gear ratios to have any benefits?

The first turbocharged cars from GM used ethanol to counter detonation.

https://www.oldcarsweekly.com/features/olds-f85-jetfire

I don't think so. Adding air (boost) also increases the amount of fuel. Doing little to change the efficiency of the reaction. Not all cars have responded positively to a warm air intake either. That could be partly dependent on the filter location itself though.

I would be curious to know if running the engine at 0 psi of boost would be beneficial.

You mean like to decrease pumping losses? With my very limited knowledge about that, I would think that this kind of slight improvement on intake side could be canceled because of a bit higher resistance on exhaust side. Maybe?

But as you say, boost equals more oxygen equals more fuel to burn, so it could be the situation that any modification that increases power needs longer gear ratios to make any good for fuel economy. With boosted air you don't have to open throttle that much to maintain certain speed, but the amount of air flowing to chambers is same, so the amount of fuel is aproximately same. Or could be?

It'll be more efficient at high load if you can radically modify the cam profiles or have variable valve duration. A turbocharged "Atkinson" cycle engine is essentially a turbocompound engine (turbocharger takes over compression duties, cylinder is used more for expansion than compression).

The problem is with most engines, ANY boost even on high duration race cams is going to be more torque than you need to cruise.

You need VVEL/Valvematic/Valvetronic/Multiair to be able to cut volumetric efficiency enough, but at low load the exhaust has less waste energy and the engine's friction is the greatest source of loss so the improvement will be very minimal.

Great question and I've tested this on my Talon.

Ethanol takes about 40-50% more fuel for the same power. So, you will use more of it then petrol at the same A/F ratio equivalent.

Even increasing the engines compression will give you a very limited increase in efficiency.

The only way to increase FE at 7psi is to run a lean-burn engine.

On my setup I can run 7psi at 20:1 A/F ratio on petrol.

At 7psi with a 20:1 A/F at a BSFC of .45 lb/hr vs 7psi with a 12.5 A/F ratio at a BSFC of .55 the gain in torque is around 12 ft/lbs. The amount of fuel saved is 18 lbs/hr. around 3 gallons with a gain in torque of 12 ft/lbs. This is a petrol-to-petrol comparison at 3500rpm loaded on a 2.0L. engine with a total 100 ft/lbs of torque at the BSFC of .45 lbs/hr.

So, with the above example you could lower the boost to say 6psi and still have the same total amount of torque and increase the FE.

With a lean burn engine at this low rpm you have to increase tumble and swirl due to the low velocity of the air and a bunch of other modifications to make this work.

Forgot to add this as you can see its 100 ft/lbs of torque total so this would be used only to climb a hill or getting up to speed on a on ramp etc.

Great answer from pgfpro.

Most cars lose a lot of efficiency under boost because of two things:
1) They need to retard ignition timing.
2) They need to run rich.

They also lose efficiency overall because 3) they need to have lower static compression ratios.

All three items are to fight detonation. Additionally, higher intake air temperatures also make detonation more likely, resulting in the need to pull more timing and add more fuel.

Running a sufficiently high octane fuel would fix this. Lean burn additionally reduces combustion temperature.

Get detonation under control, so you can avoid running rich, and keep spark timing optimal, and you should see decent efficiency gains both from harvesting exhaust energy with the turbo, but also from increased cylinder pressure and effective compression. Low static compression ratios can be worked around by running Miller cycle (effectively Atkinson cycle + forced induction).

Sounds like 1980s GM cars that were turbo charged, but they didn't use ethanol.

Lot of great information, but that's the thing, I guess? Engine should have certain qualities and needs serious remapping. But, all in all, with ethanol fuel most efficient engine could be a boosted one. Even if it have to be build from scratch with that in mind, one will not make any more miles pet gallon just bolting a Garret on and filling tank with E85. Anyhow, interesting. In big picture ethanol is so marginal, that I think that there is no pure ethanol engines from major companies.

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E85 Vehicles

E85 Vehicles



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Yes, there is lot of flexfuel cars, I know that. But most efficient ethanol engine is not flexfuel, it compromises too much. Compression ratio, ignition timing, boost pressure etc.. I don't know, could it even have smaller radiator? Of course lot of variables are ecu controlled, but I very much doubt that flexfuel engines very aggressively changes for example timing or boost pressure debending on fuels ethanol contet. They could, even should, thou?

Edit: What I mean, is that typical flexfuel engine is efficient when used petrol fuel and quite ok with ethanol. A pure ethanol flexfuel engine would be an engine, that is efficient with ethanol but petrol option could be some kind of "limb mode", that engine is able to run with it, but very ruined ignition timing and with very high f/a to avoid pinging. Do anybody get, what I'm thinking?

Some folks in my country converted gasser cars to ethanol while turbocharging it back in the day, as it was a cheaper way to overcome knock. But I wouldn't advise anyone to get rid of an intercooler, even though bypassing it as as cold-start aid might be a reasonable approach.

On my setup I have done the testing with E 100 Ethanol, E98 Ethanol, E85 Ethanol and GEM 38, GEM 40 and now testing GEM 47.

as Ecky posted above on my setup this is pretty much my engine type.
When I tested E100 Ethanol and petrol at light load Freeway testing, petrol always was a major winner when it came to FE. Now when it came to mid load the gains we're with Ethanol due to its knock resistance, but the Freeway amount of driving time was around 95% compared to the mid load needed.

So, it really comes down to you are trying to overcome Ethanol's numerically lowering heat value compared to Petrol. You can build an engine with high compression dynamic or static but in the end the heating values do matter.

These are just my opinion's so if you really want to build a engine that is for FE on Ethanol please do. Thinking out side of the box is always a great thing:)

https://afdc.energy.gov/files/u/publ...ison_chart.pdf

Thanks everybody! There is great knowledge there, and absolutely great to hear what people have experienced.

As I wrote in start, right now I'm not going to build complete engine, but only changing to ethanol. Was thinking, if there is a way to overcome lower energy content. Well, there is no an easy way, if any way at all.

So, for now I'll stay n/a and try to avoid burning any oil based fuels, as they are mostly from our eastern neighbour which I don't want to fund for their latest acts. I'll burn happily local brewed booze made of side streams of food industry, even if my mpg dropd to somewhere around 30.

I'd always thought of Vodka as tractor fuel made from potatoes.

Oh that makes total sense. I wouldn't want to fund them also. I'm running mine on paint waste solvent and soon E98 made from distilled fruit.

Alky is lower specific energy content than gasoline. You are comparing apples to pineapples. Convert gasoline mileage to the Alky equivalent (say 10% less), and beat that number.

If I ran monomethyl hydrazine and nitrogen tetraoxide, my mileage would be out of this world high, pun intended.

As long as it has at least 80% alcohol by volume, it may burn. Otherwise it could still eventually be used as a supplemental water + alcohol injection :D