Is an Intercooler Worth It for Naturally Aspirated Engines?

[Camron201]

I'm trying to find out the HP percentage gains per degree of colder air. I'm thinking of implementing an intercooler on a naturally aspired race engine. I am trying to figure out if the power gains would be enough to out weigh the flow restrictions of an intercooler. Any rough numbers would be greatly appreciated.

 

[xxChrisxx]

The power gain from cooler air alone isn't that much (due to temperature), the majority gains come from the increased density of cooler air allowing you to burn more fuel.

The reason why intercoolers are used on forced induction motors is becuse the compressing process increases the temperature of the air (decreasing density) the intercooler then brings this temerature down (increasing density).

There wouldn't really be any gains from an intercooler on a naturally aspirated engine because the air doesn't really heat up that much between inlet and inlet manifold. For a N/A engine a ducted cold air intake would do more.

 

[Mech_Engineer]

I'm trying to find out the HP percentage gains per degree of colder air. I'm thinking of implementing an intercooler on a naturally aspired race engine. I am trying to figure out if the power gains would be enough to out weigh the flow restrictions of an intercooler. Any rough numbers would be greatly appreciated.

You can't gain horsepower on a naturally aspirated car with an intercooler because the intercooler won't cool the air below ambient temperature, which you would have been taking in anyway. What you need is a cold (cool) air intake- make sure your air intake is not taking in air heated in the engine compartment.

Intercoolers are used on forced induction applications because air's temperature rises as it is compressed- cooling it off after compression can increase the air's density and reduce the chances of pre-ignition when the fuel/air mixture is compressed in the cylinder.

 

[Camron201]

I understand why intercoolers are usually used on turbo/super charged applications. Why couldn't you cool the air below ambient temperatures?

 

[Antiphon]

I suppose you could.

In fact, you could make a carburetor that took in liquid oxygen.

No matter how it works out, this going to make a great you-tube video.

 

[Mech_Engineer]

I understand why intercoolers are usually used on turbo/super charged applications. Why couldn't you cool the air below ambient temperatures?

Because an intercooler is just a radiator- it has ambient temperature air blowing across it. To get it to cool lower than ambient you would need extra stuff like a refrigteration system, or the simplest solution might be water spray to take advantage of evaporative cooling. But then you have to carry a bunch of extra water which is heavy (#1 enemy of a race car).

I suppose you could.

HOW do you propose an intercooler would cool below ambient temperature?

 

[Camron201]

I was thinking of running something colder through the cooler to cool the air. I've been looking at water, freon, alcohol cooled by dry ice, and liquid nitrogen. I am just exploring the idea and trying to learn if super cooled air would be beneficial enough to be explored further. Also, is there a temperature where the air becomes to cool for fuel atomization?

 

[Mech_Engineer]

I was thinking of running something colder through the cooler to cool the air. I've been looking at water, freon, alcohol cooled by dry ice, and liquid nitrogen.

What you're proposing would not be an "intercooler," it would be a refrigeration system. For the cost of a custom refrigeration system, you could easily go to forced induction, which would net much larger gains than cooled air.

I am just exploring the idea and trying to learn if super cooled air would be beneficial enough to be explored further. Also, is there a temperature where the air becomes to cool for fuel atomization?

Well keep in mind engines run fine in sub-freezing weather, although the air does get heated in the intake before it gets into the cylinder.

The calculations to figure out how much cooling intake air charge would affect air density exist; it could be modeled as an isentropic process as a first step http://en.wikipedia.org/wiki/Isentropic_process

For example:

$$\frac{T_{2}}{T_{1}}=\left(\frac{\rho_{2}}{\rho_{2}}\right)^{\left(1-\gamma\right)}$$

Using this equation, and knowing that gamma is around 1.4 for air, you can find the density ratio you would achieve given some cooling amount. Keep in mind that absolute temperature has to be used in this equation, that means temperature units in Kelvin or Rankine.

Also keep in mind that even if you supercool the air taken in, it will be warmed in the engine because the cylinder is hot from the previous combustion! I think you'll find that this is a waste of effort when compared to forced induction for a hp/$ basis.

 

[Camron201]

Thanks for the insight Mech_Engineer. I see how this would be more of a refrigeration unit. Forced induction is illegal in my racing organization. I am trying to think of new ways to get more power within the rules.

 

[Mech_Engineer]

Thanks for the insight Mech_Engineer. I see how this would be more of a refrigeration unit. Forced induction is illegal in my racing organization. I am trying to think of new ways to get more power within the rules.

Your best bet would be to look into:

• Cold air intake (if you don't already have one).
• Weight reduction
• Engine modification/tuning

A cooling system for your intake air is not going to be worth its weight in horsepower, especially when you consider added weight affects handing and braking as well as acceleration.

 

[Camron201]

This cooling system is going to be on a racing motorcycle. It has cold air intake, the engine is highly modified, and weight has been shaved off every where. The bike has a 212lbs wet weight with roughly 50hp. If I could make a cooling system that weighed 5lbs and made 10% HP gains, the power to weight ratio would go from 4.24lbs-1hp to 3.94lbs-1hp. We would be very happy with that much gain. I am trying to figure out if 10%+ HP gains are possible with supercooled air. For now let's say cost is not an issue.

 

[xxChrisxx]

10% is pretty optimistic from cooled air. You've also got to realize that your cooling will have to come from an air conditioning system, which you'll have to power somehow.

Look at injecting a bit of methanol (if there is no spec fuel) or even water, to get the real gains you'll need to increase compression.

For something as obvious as cooling air, you've got to look at other similar types of motorsport and ask why haven't they done it. (It's certainly not becuase it's not been thought of before).

 

[mender]

The rule of thumb with the average V-8 is 1 hp for every 10 degree (F) drop in intake air temp. That works out to about 1% for 30 degrees.

I think you'd be very hard pressed to get 60 degrees and that would likely only get you 1 hp - not a very good return for the weight and expense.

 

[mender]

I am trying to think of new ways to get more power within the rules.

What class, and where can we look at the rules?

 

[Camron201]

Here is a link to the rule book, the engine rules start on page 22. http://www.amaproracing.com//assets/AMAPro-MX-2011-Rules.pdf
We will be competing in the 250 class on a 4-stoke. The bike is fitted with EFI stock.

 

[mender]

Not much room in the rules. Get a good engine builder and go on a diet!

 

[xxChrisxx]

I'm at work so I've skim read the regs, but from a first glance I've noted the following.

If cost isn't an issue you could look at getting the engine blueprinted.
There is also slight room for with the fuel as it allows oxidisers, but messing with fuel is probably too tricky.

It also calls for homologated engine components but does specify that you can add and remove material. Leaving room for a skimmed head and compression increase. It also says nothing as to the inlet system, or engine rpm.

There seems to be one area for 'exploit'. If you have a water cooled system, you are permitted to top up the water after racing but before scrutineering, it says that the type of cooling must be the same as the standard but doesn't specify quantities. The obvious thing to do is to have a secondary tank for cooling that dumps the coolant (or uses it in some other way) at the start of the race, leaving just enough to cool the engine. Then you can top up the water before weighing. That's beyond the grey area and in the realm of outright cheating, as there is no other reason for doing it apart from running underweight.

 

[mender]

Quite a list of mods are possible but you have to know what you'll be teched on. Example: exact placement of the cylinder head wrt the bore can affect output; one of the many tricks a savvy engine builder can utilize and is undetectable without precise measurement. But that will get you booted if it's on the list to check during a tear-down, so know your boundaries and work within them. Relocating the fuel injectors can have a positive impact on hp as well but again only if allowed.I'm assuming you've done the obvious things like porting, proper cam selection, etc.

A good engine builder is a wonderful thing.

 

[mender]

There is also slight room for with the fuel as it allows oxidizers, but messing with fuel is probably too tricky.

That usually refers to the amount of alcohol (specified) that is allowed; that can add up to 5% with the appropriate mods. Rejetting on a dyno and use of a weather station at the track is necessary if the racer is serious.

 

[Camron201]

The engine is heavily modified.
-Cosworth 14.1-1 piston
-Cosworth cnc porting
-Beryllium valve guides and seats
-7 angle Newen cut valve seats
-one piece DLC coated titanium valves
-Carrillo Con rod with balanced crank
-ASF transmission process
-custom cam and valve springs
-custom exhaust
-throttle body is moved 10mm closer to head
-custom efi programming
For fuel we run VP mr-pro5. Its the best legal fuel we have run, haven't really tried changing the fuel ourselves any.
And for weight, the whole bike is fitted with titanium and aluminium bolts. As well as cnc aluminium brake calipers, along with tube less tire systems.

We have been testing valves with dimples on the backside to get more flow. It uses the same theory as a golf ball. We are always looking for ways to improve.

 

[Camron201]

Rejetting on a dyno and use of a weather station at the track is necessary if the racer is serious.

We are very serious, remapping the bike just for different tracks to account for more hills and or faster slower sections. And of course for the weather and engine mods.

 

[Camron201]

Example: exact placement of the cylinder head wrt the bore can affect output;

What do you mean by this? Will you please explain.

 

[mender]

Offsetting the cylinder head can unshroud the intake valves and improve breathing. Also, moving the fuel injectors to above the intake bell sometimes helps. If you have a four valve engine with two intake lobes on the cam, moving the lobes slightly out of phase can induce swirl and help the mid range. No guarantees but maybe some things to check.

I haven't seen dimples help unless the fuel is falling out of suspension. Do you have access to a "wet" flow bench, preferably one that measures swirl?

 

[Camron201]

Thanks, I appreciate the advice.

 

[Camron201]

Do you have access to a "wet" flow bench, preferably one that measures swirl?

I don't have access to one readily, but I could get to one.

 

[jack action]

You can cool the air 2 ways on an NA engine: http://www.speedmaxperformance.com/iceTube.php".

The ice tube is a more complex system and, according to the previous link, gives about 5% increase in hp (check the un-boosted part of the test at lower rpm).

According to the previous link, the fuel cool can seems to make a 1-2% increase on an EFI engine and it is a much simpler system (more details http://blogs.superchevy.com/6274849/chevy-tech/keep-your-fuel-cool/index.html"). Google «fuel cool can», there are many other manufacturers. Doing quick calculations⁽¹⁾ seems to agree with such numbers.

For the fuel cooling, I'm sure you can do better with a carb than EFI as there is no excess fuel returned to the tank. (Maybe adding another heat exchanger between the return and supply lines?)

Another advantage of the cooler fuel is that it will help prevent auto-ignition, hence possibility of raising the CR (if you have enough cooling for the entire race) and further increase your power output. Water or water/methanol injection would do a similar effect.

⁽¹⁾ Without accurately verifying those statements (but they seem reasonable), I obtained 2-3 % increase by using the equations from https://www.physicsforums.com/showpost.php?p=3240989&postcount=8":

Air has about half the heat capactity of fuel and you are running 12 times more air. Assuming that the amount of fuel vaporized does not change, I would expect that each deg of fuel cooling would yield about 1/6 degree of charge cooling.

 

[Camron201]

Thanks for the links and the numbers. I think I am going to make fuel/air cooler, and give it a try. My plan is to have is to have a tank with a copper or aluminium coiled tube in it for fuel cooling. I would also run a line off the tank through a small pump to an air cooling device, such as the Ice tube or a radiator, and back to the tank. I think I will try alcohol as the cooling liquid, with dry ice to cool the alcohol. Kill two birds with one stone.

 

[mender]

Mounting the injectors at the top of the intake bell uses the vapourization of the fuel to cool the incoming air and increase the density.

The wet bench is mainly to see if you are having fuel/air separation issues and that is usually tested as part of an overall flow session. The effect of swirl can be checked by opening one valve slightly more than the other, and then switching to see which valve should open first and by how much. Fuel separation can then be checked.

Intake closing should be the same for both valves, so two different lobes will need to be ground on your cam.

 

[Mech_Engineer]

Have you considered trying a water/methanol injection kit?

http://en.wikipedia.org/wiki/Water_injection_(engines )

http://www.summitracing.com/parts/AVM-30-3000/

 

[xxChrisxx]

Have you considered trying a water/methanol injection kit?

Would this be against the rules? Although it's not in the tank, methanol would probably count as fuel.

There is nothing in the regs about using cooled fuel though. You can also use aftermarket fuel tanks so long as they are heavier. Looking to integrate the cool can idea into the tank may be worth it (hides it from the competition). You could have the fuel pick up directly into the cool can then the cool outlet can to take the fuel to the carb/injectors.

 

[Mech_Engineer]

Would this be against the rules? Although it's not in the tank, methanol would probably count as fuel.

Could be, I didn't bother taking a look at the rules. Still, he might be able to run pure distilled water to cool the intake charge and possibly get a little more "oomph" out of the engine by running more advanced timing. Water injection usually functions as an intercooler application for roots-type blowers, but it does have the advantage of increasing heat absorption in the fuel mixture.

 

[Camron201]

Mounting the injectors at the top of the intake bell uses the vapourization of the fuel to cool the incoming air and increase the density.

The bike uses a throttle body with the injector built in. We can move the whole throttle body slightly, but because of rules we can't change the injector type.

 

[Camron201]

Would this be against the rules? Although it's not in the tank, methanol would probably count as fuel.

I will talk to the next racing event dean and see if it's illegal or not.

There is nothing in the regs about using cooled fuel though. You can also use aftermarket fuel tanks so long as they are heavier. Looking to integrate the cool can idea into the tank may be worth it (hides it from the competition). You could have the fuel pick up directly into the cool can then the cool outlet can to take the fuel to the carb/injectors.

We already use an aftermarket aluminium tank to have enough fuel to make it through the race. With a good design it could be done, but the fuel tank area is pretty cramped.

 

[Camron201]

If we did run a water/methanol injector. How much fluid do they normally consume?

 

[jack action]

If we did run a water/methanol injector. How much fluid do they normally consume?

There's a lot of info on http://www.rbracing-rsr.com/waterinjection.html" and a calculator at the bottom. They say that the coolant to Fuel Ratio (Based on mass not volume) should be in the 12.5% to 25% range.

You can use water alone if methanol is illegal. IIRC, it's less efficient than the 50/50 mix but it still does the job.

To make best use of space and weight, why not use ice to cool the fuel and recuperate the water once it has melted?