General engine questions

The size of the pump doesn't make a rat's arse of difference to the flow at a given pressure drop. You still need the required pressure to get the desired flow. Most standard FI pumps can supply enough fuel at 3 bar to handle 300 bhp even when the engine puts out less than half that. What they can't do is run at much higher pressures than standard for long periods. It's the injector that limits the fuel supply at a given pressure drop, not the pump. Please stop pontificating about things you don't understand.

Then let's try and find you a workable solution. However you've posted your query on a forum where very few people are going to have the technical knowledge to solve your problem. Few injector systems are going to have 30% extra capacity in the duty cycle as you've found out. However if you achieve part of the enrichment from increased fuel pressure and part from increased duty cycle you have a solution.

Assuming the fuel system runs at 3 bar and it can be safely increased to 4 bar you gain 15.4% extra fuel from the pressure increase. You then require

1.3 / 1.154 = 12.6% extra from the duty cycle. Most systems can cope with 15% to 20% extra duty cycle so you now have a viable solution if you fit a different, or adjustable, pressure regulator. The pump output should not be a limitation because they often have 50% or more spare capacity to cope with wear and tear.

There are however some cars which run the injectors at very close to maximum duty cycle so if you intend this to be a universal panacea it might not always work. In those situations, as I said previously, your solution is to fit larger injectors.

They might well be commercially expedient. Doesn't stop them being a bodge, though.

Where did you get 30-34% from?

You can't use Higher Calorific Value (or Gross Calorific Value or Higher Heating Value) as the water from combustion doesn't condense and yield it's energy to the engine. You have to use Lower Calorific Value (or Net Calorific Value or Lower Heating Value).

21.1MJ/L, Petrol 31.8MJ/L. You need 31.8/21.1 = 1.507 timesthe volume flow rate (51% increase). The above site says 53%, nodoubt the LHV was rounded. Or you need 2.34x the fuel pressure.

It's possible to run very lean at light cruise load without doing engine damage. Reduce engine rpm, open throttle to restore power to cruise requirement and then move mixture lever lean. It's safe because the head temperature drops a lot from Lambda=1 temperature. This was used to increase operational duration of a WWII fighter bomber from 5 hours to 8 hours and still have more fuel in the tank on landing than before. It's how the B29 Superfortress did the long range missions it did and how the Lockheed Constellation crossed the Atlantic direct New York to London with 100 passengers without a splash and dash in Ireland or St Johns.

-- Peter Hill Spamtrap reply domain as per NNTP-Posting-Host in header Can of worms - what every fisherman wants. Can of worms - what every PC owner gets!

Another thought is, can a normal fuel pump designed to be run on petrol, withstand running on ethanol?

Hi again, everyone!

Looks like my posting started a hurricane... Anyways, I'M GREATFUL FOR ALL POSTINGS, though some of them were not what I expected. No hard feeling from my side. Let's shake hands and enjoy. I apologize if I were unkind to someone. Coyoteboy, adrian and who else... But some of you aren't very kind either.... Anyways........ Actually, I've run my car on ethanol over one year, and it performs very well. I'm no engine expert (the reason for posting here) and some advice are always welcome. I'm working as an electronic designer for the audio industry (power amplifiers and switchmode power supplies) but engines has always been an interesting area, especially efi. Thank you.

Want to buy a Universal Perfromance Modification?

A commercially expedient bodge if ever I saw one.

Who said I was talking about physical size?

It's quite common when talking about pumps for a 'bigger' pump to mean it can give a greater head - which is exactly what you would need here, barring replacing injectors, reprogramming ECUs etc.

Tell you what, put a bigger pump in to increase the pressure and give a higher fuel supply for the same injectors. Why didn't I say that in the first place.

Please stop making assumptions then saying I'm wrong based on them.

Maybe I don't build engines for a living, but I know enough not to try and simplistically extend the injector duty cycle 30% across the entire range and expect it to work smoothly. So that makes me amply qualified to comment.

And anyway, it's Usenet, so nurr.

Nice try but whether you really meant bigger pump or higher pressure pump makes no odds. Injectors are designed to work over a given range of pressures. 35 to 45 psi is the normal range and you might get away with 60 psi. Much more than that and they won't seal when shut and start dribbling fuel into the manifold. That's a common enough fault even at 40 psi when they're getting old or fuel deposits are building up on the pintle.

I'm almost tempted to buy one at that price just to confirm what I think it is.

And having just looked back at the negative feedback, looks like it is what I thought it was. I wonder how many people actually think it makes a difference?

It'll make a difference until the ECU enters closed loop operation, then the ECU will adapt to the new parameters dropping back to it's original power level. And it won't alter the timing on any engine that has a knock sensor fitted (that'll be most then!)

Fair enough. I never said it would work anyway, but a combination of running the injectors at a higher pressure and for longer *might* just give enough extra to actually run on ethanol. Allowing for a more sophisticated control system then the one being proposed, anyway. ;-)

Just as an aside, is ethanol the same density/viscosity as petrol? Does that make a difference to how well the injector seals etc.?

I'd assumed you were only trying to run an ethanol/petrol blend but now I'm not so sure. In fact I think you may be horribly confused about all sorts of things.

The heating value (calorific value) of ethanol is indeed about 33% lower than that of petrol but that has absolutely nothing to do with the stoichiometric air/fuel ratio.

Firstly, even if the 'energy content' was relevant, simple maths tells you you'd want 50% extra fuel not 33% to compensate for a 33% drop in calorific value.

Secondly the stoichiometric A/F ratio for ethanol is 9 as opposed to 14.7 for petrol. That means you actually need 63% more fuel by weight for a given amount of air. As ethanol has a slightly higher specific gravity than petrol the increase required by volume (which is what the injectors will meter at any given pressure) is somewhat lower than this, around 53% extra.

If you are indeed trying to run pure ethanol in your car, or even worse trying to develop a system to sell to others then you're an accident waiting to happen because you appear neither to understand the stoichiometry or even the basic maths of the situation.

It's a penny resistor.

powerampfreak ( snipped-for-privacy@hotmail.com) gurgled happily, sounding much like they were saying :

OK - would you care to answer the question about where the hell you get it from, because I've never once seen Ethanol fuel for sale in any country.

Slipping slightly off topic, does anyone remember if it was Ethanol fuel that a BTCC team said they were using at Knockhill last Sunday?

Ethanol is widely used in Sweden. It's costs less than petrol and with its 104 octance it's a good fuel for turbo engines.

I assume its a hybrid mix then, as fairly pure ethanol is meant to be

129 octane and 34% less calorific value. In most of the developed world this costs more than petrol and is only available from industrial chemical outlets, and at around 3x the price of petrol (maybe even under licence IIRC, it being toxic in small quantities). Hence many people questioning why you would want to bother unless it were for high-performance reasons. No-one wanted to be nasty in the first place - we were just offering advice - clearly you know something about electronics but you asked about engines and got told about it and then warned that engines arent as simple as just using X% increase. We were only trying to help you not damage your (or other peoples) vehicles without good understanding first. Sorry if that came across badly or unpleasant but I feel i have to warn people - ive had several undergraduate students approach me with ideas - only to come back with damage done because i expected them to research the area properly but they failed to spot simple problems they should have seen coming. J

The fuel is called E85, it's a mix of 85% ethanol and 15% petrol. Many cars in Sweden are sold as FFV-cars, flexible fuel vehicles, they accept ANY mix of E85 and petrol, so the engines have no problem with it.

Is there any other discussion forum which may answer questions, that you consider to be silly? I like to get some information from time to time, and don't know where to turn to.