Fuel pre-heater: Do they work

[ApEkV2]

While waiting for a couple of items to arrive via the mail, I began learning about fuel pre-heaters and want to know whether they work or not.
The brief science of it all is to heat the gasoline somewhere in between the fuel pump and fuel rails.
With the easiest heat source being the engine cooling system, the gas would be heated to around 180* F with the means of a heat exchanger.
This heated gasoline has an increased molecular kinetic energy, and thus mixes better with the air.

For an example, you have a jug of cold water and a jug of hot water.
It takes less time and effort to mix a solute into the hot water than the cold.

One question people ask is, "Isn't vapor lock a problem?"
Well from my understanding, vapor lock occurs when the gasoline between the gas tank and the fuel pump becomes heated creating a vapour.
The fuel pump has a hard time of drawing vapours, so the engine looses power and stalls.
I haven't heard of vapor lock occuring in between the fuel pump and the rails.

Here is a vid from youtube and some resources of what I'm talking about.

YouTube - Fuel Pre Heater Prodgect for 89 Ford Mustang

Flash point - Wikipedia, the free encyclopedia

Vapor lock - Wikipedia, the free encyclopedia

I want to know if this idea actually works, and if anyone has built one that increases fuel economy and can comment on their gains or losses.

If there is already a thread about this, I'm sorry to be a bother, but I think it's smart to revisit things now and then to keep ideas floating around.

Matt

[everwiser]

From the studying I've done on the subject it seems that the "modern" formulations of gasoline prevent all but the lightest elements of it from vaporizing causing the heavier, less ignitable, elements to "gunk up". However, I've read many articles saying that modifying the intake system to be preheated by the hot exhaust does improve fuel economy on newer vehicles.

Based on my own observations of fuel mileage on my vehicles, my gas mileage is always better in the summer when the air entering the engine is hottest and worse when the outside temps drop off. I've measured a difference of around 3 to 5 mpg between summer and winter driving.

It makes sense to me if the fuel is warmer and the air is warmer, then fuel injected/atomized will have a tendency to remain atomized and/or further vaporize whereas cooler temps in the intake/cylinder will have the tendency to condense/coalesce the atomized fuel into larger liquid droplets thus hurting the burn efficiency.

So I guess the answer is "it depends".

[dambit]

It makes sense to me if the fuel is warmer and the air is warmer, then fuel injected/atomized will have a tendency to remain atomized and/or further vaporize whereas cooler temps in the intake/cylinder will have the tendency to condense/coalesce the atomized fuel into larger liquid droplets thus hurting the burn efficiency.

Hi,

Directing "cooler" ambient air into the into the intake manifold, instead of the warmer/hot engine bay air, increases performance. That's why almost all race tuned cars have cold air induction.

Maybe I am thinking of power performance and not fuel efficiency.

Cheers,

Steve.

[ApEkV2]

Using cooler air does increase performance. The reason being that cold air is more dense than hot air.
For example take a balloon and fill it with air. Now heat it up. It expands, and when it is cooled, it gets smaller.
So the cold air occupies less space than the hot air (when inside a container).

Building a preheater is not that expensive at all. Just find some scrap copper, a couple of brass barb fittings and solder it together.
I will probably do this in the near future.

[wpage]

Both work

The hot and cold dialog on fuel and air has been going on for some time and there is research to support each position on air. I do believe that both hot and cold air have thier place in a air system for optimal performance.

For fuel I have never seen anything supporting cold performance.

Therefor it seems worthwhile to explore further fuel pre-heating since it does show promise

[everwiser]

Getting more air into each cylinder (which is easier with cooler/cold air as it's denser) does increase performance but it also increases the fuel demand else you'll end up running lean and under full power/load the detonation/pinging will destroy your piston rings and/or ring lands. Max fuel economy and max engine power do not necessarily go hand in hand (nor are they mutually exclusive).

Modern vehicles will automatically lean the fuel mixture if the intake temps are higher (at least to limit of their programming) so by preheating the air entering the engine you're killing two birds with one mod. The warmer air will cause the computer to deliver less fuel (better mpg) and if the fuel vaporizes better in the warmer intake air, the oxygen sensor will detect a "richer" mixture and then lean the fuel mixture even further.

There is no free lunch. You'll have to decide what you want. If you want max power you're hurting fuel economy. If you want fuel economy, you'll be hurting max power. Some have had some success using the MegaSquirt controller and developing dual fuel maps for switching between power and economy but you can only do so much and maintain drivability. A freer flowing exhaust will give you more power and top end but will require more fuel to compensate for the better cylinder filling that less backpressure creates. I know I'm contradicting myself but it really comes down to the type of engine you're modifying and how you're modifying it. If engine mods make the engine more thermally efficient then it might help both power and economy. It just really depends...

If you have long freeway runs where you can keep your foot out of it, you can use an EFIE system to lean the fuel out on the fly. As long as you don't have to pass or climb any big hills, you can probably gain some MPG using this method and then turn it back to "normal" for stoplight action.

Just an FYI. Most of the "power" kits for cars you see on Ebay or the internet for dirt cheap are simply a resistor kit that varies the intake air temp signal going to the engine computer. Turn the resistor up and the computer thinks the air is cold and richens up the fuel curve. Turn it way down and it thinks the air temp is hot and leans out the fuel curve. To far either way and a person can end up with more problems than they need.

[rmay635703]

One simple reason that warm air helps is because pumping losses are reduced, it does sap a lot of power from your engine when the butterflies aren't fully open! Since most folks rarely run anywhere near full throttle the more you can open the intake and reduce pumping losses the better you will be.

[dave_cahoon]

Group,

Most engines will get a few % from rainy days.
Because the moisture in the air.
There are airstone devises out there for sale,
that mimic a rainy day...

Dave

[ApEkV2]

That is an awesome idea Dave. I was also thinking of a water mist spray into the intake.
I was going to use an oil burner nozzle (.016 gallon per minute rate or lower), but this idea sounds better.
Now I'm going to have to try both!

[dutchdivco]

Best source for fuel economy info

Google MPGRESEARCH. They cover fuel heaters, intake heating and cooling, Somenders grooves, H2o injection, and much more! You can spend several hours reading all of the threads, in all the different topics(much like this site).Unfortunately, the sites been kind of dead lately, and they are slow to respond to attempts to join. But, you don't need top be a member to read the threads.
In my opinion, and from my experiance; If mods for fuel economy is where you want to go, start off with a pre-70's car.You can find them, cheap, if you shop around.Pick one where the model and engine were made for at least 10 years. In that case spare parts will still be available. Example; Ford 223 inline 6, made from '54-64.I can get any part for the engine I need, and have a complete engine worth of NOS parts. Set of pistons=$100.00, set of pushrods, same.
I believe that once you get into fuel injected, ecu controlled with a catalyctic converter, the engine tends to fight you, as almost any mod you do to improve economy is going to confuse the O2 sensor, and the ECU will richen the mixture, to make sure there is enough unburned gas in the exhaust to make the catayctic converter work.To me thats an insane, ass backwards way to do things.
Specifically regarding fuel heating, I DO have a 'modern' car; '89 Camaro,2.8L.I noticed early on the fuel lines run real close to the exhaust manifold, so, on this car at least, the manufactuer is already heating the fuel, and I'm sure they did it on purpose.And, the stock intake IS a 'cold air intake'. Thing is, they were trying to meet emissions standards, get some economy, give some performance, and were locked into a certain way of doing things based on; decisions previously made and courses of action committed to, institutional inertia, etc.Anyway, my 2 cents worth. Jim

[everwiser]

It depends upon the level of control and sophistication you're looking for. In my previous post I mentioned the MegaSquirt. These can be assembled by the do it yourselfer or bought completely assembled with the end user putting together their own hardware in the configuration they choose. This opens up the "black box" aspect of engine controls so that anyone can take over control of how their engine responds to changes. If you check out their site, there are people pursuing the entire range of possibilities, from extreme fuel economy to extreme performance. When it comes down to driving satisfaction, driveability, and repeatability, engine management systems can not be beat IMO. Of course, I'm also an EET so the programming and electronics don't bother me because the learning curve is already somewhat flattened by what I do for a living.

In the case of fuel preheating, something to keep in mind is the fuel pressure. With a carburator, fuel pressure is somewhere around 3 psi so if the fuel gets too warm, you've got vapor lock. With fuel injection, you've got fuel pressure of around 40 psi which will keep the fuel in liquid form to a higher temp than you can at 3 psi (same principle as having a pressurized cooling system). I read somewhere that your average fuel injector is good to around 400 F. I think a combination of heated fuel, heated intake air, and the atomization of the fuel injectors will achieve better in-cylinder vaporization with driveability and control than carburated vapor induction alone will get you.

There are many newer vehicles and engines that have millions of copies on the road, are dirt cheap, and have inexpensive parts available. The problem with 70's (and many 80's vehicles as well) is that you can get anything for the engine but you'll be hard pressed to find anything for the body or chassis that you will need to keep it on the road. Most salvage yards crush anything/everything that is over 20 years old unless it's a collector vehicle making it very difficult to keep such an old vehicle for a daily driver.

Just my .02.

[dutchdivco]

To each his own.

As far as availability, I'm lucky to live in a large city. I can go on craigslist, autos/trucks for sale. Type "classic car" or "classic truck" and find lots. For instance 2 mid 60's Plymouth valients are available right now. Great economy engine, the slant 6. I like the older cars where they are easy to work on, lots of space. The newer ones seem to be designed to make it nearly impossible.And, I don't have some gov't inspector sticking there nose under my hood, and telling me "You can't do that! $2500.00 fine!" Course I'm NOT real swift when it comes to electronics.Anyway, to each his own. Jim

[everwiser]

I can't argue with the "room to work" factor. I've got a 78 Chevette, and an 85 Dodge stepside I intend to "modernize" (I like easy starting when it's below freezing ). I've previously owned a 68 Beetle, 74 Karman Ghia, and a 68 Dodge stepside. The latter two were very difficult to get "the little things" for to keep them comfortable to live with. I also live where we don't do State mandated inspections so the big city (and whatever state you're in) is working against you in that regard.

It basically comes down to "each their own". I just advocate tech where possible because it truly does make life easier.

[hhoexclusive]

this is what i did. i used 3 metres of copper coil the same size as my fuel line and put this in the engine bay my engine bay can reach 80c + when i thrash my car hence no need to tap into my coolant lines. it worked a treat i got my usage from 12 litres per 100km to 10.5. i then fitted a huge hydrogen booster and got it down to 7.5 litres i also picked up around 15hp. i verified this using areal time fuel flow meter so these figures are accurate.

[ApEkV2]

People can be doing alot to increase the efficiency of gasoline engines.
The problem is the general public has a negative stereotype of fuel saving devices whether they work or not, or the majority of the pop doesn't have any knowledge of these devices.

I will be building the preheater hopefully late next week. I have other projects that pose greater benefits.

On the design I am planning, I'll try to replicate the video link in the first post.
The only difference is I am going to use far less solder than he did.
Planning on only using solder in like a spot welding manner. The thermal conductivity of silver solder is vary high similar to copper.
After the mess is all fixed up, ArmorFlex is going to be used to insulate it.
Oh and angle iron to keep it secure to the radiator.
(for this car, the best place for it on the radiator line is right next to the radiator because there isn't much room anywhere else)

After the preheater, the wet stone idea sounds good to try. Like a high speed humidifier or a ultrasonic water mister.