Electric WAI

[RedDevil]

The cold season is upon us, nipping any attempt to get good or even average FE in the bud at every cold start.
When it is freezing and I start my car and walk around it I can smell the unburnt fuel from the exhaust. Such a waste, but what to do?

What about electrically heating the intake air?
It needs to be electric; the exhaust manifiold is still cold too at first.
If I can heat the intake air by maybe 10 to 20 degrees Celsius, just until the engine is lukewarm, it will aid the combustion producing more heat, it will reduce pumping loss by being less dense, burn cleaner, rev lower, etc.
Investing a few hundred Watt to make an engine that consumes over 10 kiloWatt worth of fuel run maybe 5% more efficiently would make sense.

This has been lingering in my mind for a while. I believed it would not make economical sense but promised myself to do the math to prove it does not make sense.
So I just did the math, helped by the data in Wikipedia's earth atmosphere article.
And much to my surprise it seems possible after all.

Here goes:
Take a typical 2 liter engine running stationary at 1200 RPM at 50% load. I focus on low revs/low load because that's where the combustion is worst in the cold.
Each cylinder would have 600 intake cycles at half atmosphere per minute, so it uses 600 liter of air (atm) per minute, or 10 per second.
It takes just over a kJ to heat a kilo of air by one degree Celsius.
The air density at sea level at temperatures just below freezing is about 1.4 kg per cubic meter or 14 gram per 10 liter.

So we would need just over 14 Watt to heat the intake air by one degree Celsius on this engine. A 140W heater could raise it by 10 degrees, 280W would do 20 degrees. For that 2 liter engine; mine is smaller and could do with less.

This is something I'd like to try out, if only I knew how to do it.
First of all, what heater? Camping and caravaning shops sell 12V 150W blow driers, that could be something; maybe it could even just fit the intake pipe. There are ceramic heaters, Peltier elements, you name it.

Then where to put it? I'd like it behind the air filter, as I don't want to waste time and energy heating that up. But then it has to be small enough to fit in between the filter and the throttle house. It needs thermal protection, don't want to melt the OEM stuff around there.

Finally, when to switch it on? Manual is the easy way, but it is useless when the engine is warm so a bimetal switch on the block makes sense. Then of course the overheating protection.

So, your thoughts please.
Am I reinventing the wheel? Saw nothing on eWAIs here, but might have missed it.
Do I miss something, is there a fault in my logic?
I believe the system can take another 150W, especially in the hands of an ecomodder. Yes I changed the incandescent bulbs for low-power LEDs and HIDs, and do not use the rear defroster in the first minute thank you, and might even leave the audio off if I'm in really the mood. And it would be another incentive to build a PHEV booster pack. Ah.

Laid my egg, now shoot

[gone-ot]

Air goes IN, then goes OUT.

OIL stays IN, goes round & round, but stays IN.

Warm OIL is far better than warm AIR...to start with.

[RedDevil]

I get that, but it takes much more energy to heat up all of the oil (and engine parts) than just the intake air if raising the pre-combustion temperature is the goal you're after. Which I am.

I see the benefit of heating oil. Let nothing distract from that.
Even so, there is a time and place for other systems like heating the intake air. I see my car heat up pretty quickly, but in those few miles it just wastes a lot; those few miles are my target.

The air that gets out passes the catalytic converter first, which only works well when hot enough. Badly burnt cold exhaust gas is a double reason for preheating the intake air.

[t vago]

Actually, it's not a bad idea. Certainly worth a look. I found an electric cabin heater on Harbor Freight for $10. You might could modify that for your electric heating needs. It may be a good idea to put some sort of a screen after the heater elements, though, so that loose bits (which might form after several months) would not get sucked into the engine itself.

[Frank Lee]

I saw the maths but did not digest all of that; it just doesn't seem to me that a modest electric element would contribute enough. I'd look into a propane torch heated pre-chamber ahead of the air cleaner, for safety from explosion's sake.

Or better yet, grille block + engine blanket + core plug heater = preheat all that metal mass and surrounding zone which surely would warm the intake charge some.

[mort]

Originally Posted by RedDevil

So we would need just over 14 Watt to heat the intake air by one degree Celsius on this engine. A 140W heater could raise it by 10 degrees, 280W would do 20 degrees. For that 2 liter engine; mine is smaller and could do with less.

I think 50% load is pretty high. But a little cold water: what is the temperature rise due to compression?

-mort

[XYZ]

Originally Posted by RedDevil

The cold season is upon us, nipping any attempt to get good or even average FE in the bud at every cold start.
When it is freezing and I start my car and walk around it I can smell the unburnt fuel from the exhaust. Such a waste, but what to do?

What about electrically heating the intake air?
It needs to be electric; the exhaust manifiold is still cold too at first.
If I can heat the intake air by maybe 10 to 20 degrees Celsius, just until the engine is lukewarm, it will aid the combustion producing more heat, it will reduce pumping loss by being less dense, burn cleaner, rev lower, etc.
Investing a few hundred Watt to make an engine that consumes over 10 kiloWatt worth of fuel run maybe 5% more efficiently would make sense.

This has been lingering in my mind for a while. I believed it would not make economical sense but promised myself to do the math to prove it does not make sense.
So I just did the math, helped by the data in Wikipedia's earth atmosphere article.
And much to my surprise it seems possible after all.

Here goes:
Take a typical 2 liter engine running stationary at 1200 RPM at 50% load. I focus on low revs/low load because that's where the combustion is worst in the cold.
Each cylinder would have 600 intake cycles at half atmosphere per minute, so it uses 600 liter of air (atm) per minute, or 10 per second.
It takes just over a kJ to heat a kilo of air by one degree Celsius.
The air density at sea level at temperatures just below freezing is about 1.4 kg per cubic meter or 14 gram per 10 liter.

So we would need just over 14 Watt to heat the intake air by one degree Celsius on this engine. A 140W heater could raise it by 10 degrees, 280W would do 20 degrees. For that 2 liter engine; mine is smaller and could do with less.

This is something I'd like to try out, if only I knew how to do it.
First of all, what heater? Camping and caravaning shops sell 12V 150W blow driers, that could be something; maybe it could even just fit the intake pipe. There are ceramic heaters, Peltier elements, you name it.

Then where to put it? I'd like it behind the air filter, as I don't want to waste time and energy heating that up. But then it has to be small enough to fit in between the filter and the throttle house. It needs thermal protection, don't want to melt the OEM stuff around there.

If you heat the airbox, you automatically will heat the air that is in the box, to some degree.

I agree, don't introduce any heating elements into the OEM system that might melt anything. How about using a cheap 12v seat cushion warmer, wrapped around the airbox? It wouldn't hurt anything and it might help warm intake air. It makes for an inexpensive experiment. It would be easy to control the on-off function of the blanket heater, either directly by a switch or by a thermostat.

[t vago]

Originally Posted by mort

I think 50% load is pretty high. But a little cold water: what is the temperature rise due to compression?

-mort

You're probably looking at a temperature rise of around 150 K. However, that's only going to affect the gasoline that's still suspended in air. What about the gasoline that sticks to the combustion surfaces?

[JRMichler]

I'm convinced that the bulk of the cold start reduction in mileage is due cold oil. That's why engines crank so much slower when it gets cold. An electric WAI would not help.

Don't some diesel engine have electric WAI? If so, find one of those in a junkyard. It's designed for under hood use.

[NachtRitter]

The question I would have is what is causing the unburnt fuel... is it because the computer is enriching the fuel mixture when the engine is cold? And if that is the case, what is the computer using to determine when it should enrich the fuel and when it can stop enriching the fuel. Is it based on the intake air temp or is it based on the coolant temp... or is it a combination? Although I don't have the answer, I suspect it has to do with the coolant temp more than the intake temp... so the faster you can get the coolant up to temperature the sooner the enrichment is stopped. Yes, a higher intake air temp will help warm up the engine faster, but I suspect the difference in time is going to be negligible. Getting the block up to temp using a block heater will have a much greater effect.

Also, if you are powering the heater off your own engine, aren't you loosing some of the efficiency you are trying to gain? Unless you are able to do an amazing insulation job around the heating element so that 100% of the heat generated is being transferred to the intake air, you'll be losing some of that heat that you're generating into the atmosphere (well, to the engine bay which is open to the atmosphere, in effect)... so the 280W heating element may raise the temp of the incoming air by some amount, but not necessarily 20 degrees... the element has to heat the air plus the surrounding ducting which is being constantly cooled by the incoming air and the cooler air in the engine compartment.

Personal opinion (gut feel, no data, so take it for what it's worth) is that you'll get the most bang for your buck out of a block heater that you plug in at home.

Originally Posted by JRMichler

Don't some diesel engine have electric WAI? If so, find one of those in a junkyard. It's designed for under hood use.

In the case of my TDI, there are glow plugs in the coolant line... the purpose being to accelerate the heating of the coolant. Not sure if other diesels use electric WAI.