Fuel & coolant temp effect on power?

[Kometes]

Hi All,

Just wondering if anyone has any calculations, rules of thumb, resources etc for showing the power loss/gain based on the temperature of fuel and coolant?

I'm also looking for some resources for radiator design based on a known heat rejection required, I know there are some good spreadsheets around but can't find any.

Cheers,

 

[patprimmer]

Power change from intake air temperature variations can be reasonably calculated by the combined gas laws so long as the charge does not get so cool as to inhibit ignition.

Fuel temperature has an insignificant influence due to the low mass of fuel in the charge relative to the mass of air. The very small amount could be very inaccurately calculated by specific heat and mass and temperature difference, but the amount of heat transfer from fuel to the air between the time the fuel is injected into the charge and the inlet valve closes would be very difficult to calculate.

Influence of coolant temperature depends on many other factors such as surface area to volume ratio, compression ratio, engine speed, to name a few.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[Lou Scannon]

That about sums up the temperature effects, Pat!

The realities of designing and manufacturing just about anything with any degree of complexity to it, such as a radiator, are such that no-one is going to get it right the very first time. You'll have to experiment, and feed the results into subsequent designs.
You might consider shopping for an off-the-shelf radiator, for your your known heat rejection case.

I forgot what I was going to say

 

[ivymike]

fuel temp does result in derate on diesel engines (not electronic derate), and I thought it was because you were injecting less fuel as a result of thermal expansion.

On a turbocharged diesel air temp can affect cylinder pressure in an important fashion (because charge density is higher) even if output power isn't much changed (constant fueling). This can be a problem with diesels operating near their limits in cold climates, or on/near startup of just about anything in an extremely cold climate.

 

[GregLocock]

I believe the experience with stock engines is that the main effect from increasing coolant temp slightly is a slight increase in EGT.

Having said that I worked on a gasoline->diesel conversion and the fuel consumption was ridiculous as the head was too cold.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[patprimmer]

Sorry Isaac you are correct, I just presumed spark ignition and it is entirely possible he may mean diesel or even either or.

I said to cold can inhibit ignition, but to hot can induce detonation or preignition.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[catserveng]

If you're dealing with diesel engines CAT has a publication called Engine Installation and Service Handbook, form number LEBV0915. On page 56 of the one I have it has correction fators for performance analysis rules of thumb. I have used these factors on other brands of engines as well and found them to work out pretty good.

I don't have a PDF version of this but your local CAT dealer may give or sell you a copy.

Hope that helps, Mike L.

 

[Kometes]

Thanks for your responses. This is for an unleaded I4 race engine, just looking to squeeze any extra power from it.

 

[patprimmer]

Is compression ratio free. If not what is the spec. I presume you have already optimised CR and quench.

Fuel temperature is pretty much irrelevant unless you are trying to squeeze more into a restricted tank size to reduce the number of fuel stops.

Increasing coolant temperature increases power if detonation is not an issue, however I suspect it is and I would expect you need to test your specific set up to determine a:f vs ignition timing vs coolant for the optimum compromise. I am sorry I can't be more help.

Even if hotter coolant with richer mixture allows you to not pull timing so you do increase power, you need to weigh the power gin vs the extra average fuel load.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[SomptingGuy]

What's the displacement of this engine? Are there any artifical physical constraints that might limit airflow?

- Steve

 

[Kometes]

Compression ratio is fixed at 9.75:1. Most of the internals of the engine are fixed and it's a 1600cc engine.
It's rear engined with the radiators sitting in side pods, we're looking to minimise the size of the opening in the side pods if at all possible to reduce the drag.
The fuel tank is ridiculously oversized for the duration of the races so there's no need to increase the density in order to fit more in, your point about it being such a minute amount in comparison to the volume of air does make quite a bit of sense Pat.
Timing cannot be changed so I don't know that running it too much hotter is an option.