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Old 03-19-2017, 11:59 AM   #1 (permalink)
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Warm Air Intake With Steam

After reading this thread:
I May Be Wrong About Water Injection WRT Improving Fuel Economy

and many others i have started to ponder. I want to do water injection to my engine and wondering if steam injection would have any benefit at the moment.

Then i started thinking, warm air intakes are generally a good idea, to make them better, it would be beneficial to be able to control how much heat is added to the system. Then I started thinking that I could use steam to heat up the warm air intake, it would not take much steam at all to heat up the air. And I can control the amount of steam to with respect to airflow to get a relatively precise heated air flow.

My system, although crude in conception at the moment is as follows:

Wrap stainless steel or copper pipe around the exhaust manifold. Run a thin hose (PTFE or silicone) that is heat tolerant to the air intake. On the other side of the pipe, connect a short length of hose that will act as a heat break and improve flexibility to the end of which i will be adding a gasoline/ethanol injector. The injector i can control based on MAF and RPM or other data that I receive from the canbus.

Injecting a certain amount of water will make a certain amount of steam come out of the other side. If i can make the flow uniform enough, it will deposit the heat in to the air.

This idea plays wall with cold air intakes, as the air can be heated up nicely and the heat input can be stopped immediately if cold air and more power is desired.

But how much water would i need to inject per volume of air...

I am starting to do some calculations, so i wanted to start a new thread so my calculations are not lost (as they usually are).


For this i will use one of my least favourite units for energy, and that is a calorie.
1 calorie -> energy required to heat 1 gram of water by 1 deg C.
To boil water you need 540 calories per gram.

(i hate calories because the diet industry has started to use it, and as they are generally idiots they have redefined Calorie (with a capital C) to mean kilocalorie, and different tempreatures of water require diffent calories to heat up. So a 4 degree calorie is not the same as a 90 degree calorie, {I am a metric person so unless specifically indicated, all measures are in C.}

This site has good info on many things:
Air Properties


Air has a density of 1.3 kg / m^3 at 0 deg C, and 1 kg at 80 deg C.

I will use 1 for now so calculations are simple. So 1 kg of air is 1m^3. This can be refined later on.

Specific heat of air is roughly 1 (kJ/(kg K))

-> 1 kJ to heat 1 kg of air by 1 deg C (or Kelvin, when they are relative they are the same unit).

So, I will need roughly 1 kJ of energy to heat up 1 kg or 1m^3 of air.

So roughly i need 239 calories to heat up 1m3 of air by 1 degree.

Now i shall assume that my water vapor is at 100deg C, boiling temp, or it has not absorbed any more energy after it was vaporized as i do not want to add another sensor to measure the temperature of the steam from somewhere in the pipe.


---------------------------------------------------

Lets assume that i am cruising at 2000 rpm with my 3.7L engine.
I do not have a turbo and i am assuming volumetric efficiency of 100. To redo my calculations yourself you can use this site that calculates airflow, and you can plug in your boost pressures etc... :
Engine Air Amount Calculator

So at 2000 rpm, my engine consumes 4.6m^3 of air per minute.

239 * 4.6 = 1094.8 calories to heat it up by 1 deg (per minute).


Lets assume that the outside air is at 20 degs C and i want to bring it up to 80 deg C.

60 deg C temp difference so:

65688 calories are needed per minute. ( I have calories so:

Divide that by 540 we get 121 grams of water vapor are needed. (At time of injection it will be about 200 liters of steam (0.2 m^3) per minute, but as per our calculations after it has given out all of its energy, it will be in water droplets at 100 deg C, taking up a volume of 121 ml.




Just to check feasibility, that would roughly make: 7.26 liters of water per hour.

So there you have it, my back of the napkin calculations.

A lot of the calculations will have to be more precise on the microcontroller, and i will plug in the correct numbers when doing the calculations and obtaining the delta T calculations. I think i will probably also need to measure the temperature of the steam.

So how does it look? Any objections?

Assuming the car at 2000 rpm consumes 10 liters of fuel at 100km/h. That makes 10 liters per hour, and we would be using 7 liters per hour, so 7/10 (%70) water to fuel ratio... I am not at all sure how the engine will like this as %20 is stated as the limits of the beneficial amount of water (not steam) injection.

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Old 03-19-2017, 12:17 PM   #2 (permalink)
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Damn, just noticed i have posted in the aerodynamics forum, if a moderator would be kind enough to move it, it would appreciate it.
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Old 03-19-2017, 12:37 PM   #3 (permalink)
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Steam and Vapor Enthalpy

Steam has 1.307 (kJ/kg.K). So on a kilogram basis it needs more energy to heat it up than air (waight to waight basis).
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Old 03-19-2017, 04:53 PM   #4 (permalink)
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Hnm. Another question.

In order to see any benefits, i would need to inject pre MAF right? So that the ecu knows the intake is hot and adds less fuel.
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Old 03-20-2017, 03:51 AM   #5 (permalink)
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Not sure to which point the ECU would still be adding less fuel. Once it detects the intake stream temperature to be too hot, it might actually increase the fuel ratio in order to cool it down and decrease the temperature.
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Old 03-20-2017, 03:55 AM   #6 (permalink)
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It would need an insulated intake to help combat condensation and puddling water. How would you handle over generation of steem ,such as summer? Run it through a cooler of sum sort and jyst letit cycle?
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Old 03-20-2017, 04:10 AM   #7 (permalink)
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Quote:
Originally Posted by gumby79 View Post
It would need an insulated intake to help combat condensation and puddling water. How would you handle over generation of steem ,such as summer? Run it through a cooler of sum sort and jyst letit cycle?
Probably some return line linked to a cooler, while the steam amount added to the intake stream could be decreased.
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Old 03-20-2017, 07:01 AM   #8 (permalink)
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AMount of steam = amount of water i inject.

I have an gasoline injector where i can control the pulses, so i can precisely measure the water entry to the system.
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Old 03-20-2017, 10:28 AM   #9 (permalink)
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Quote:
Originally Posted by teoman View Post
Assuming the car at 2000 rpm consumes 10 liters of fuel at 100km/h. That makes 10 liters per hour...
This is a good and reasonable assumption, and I'm seeing similar figures with my Magnum.

So... Using this figure, and assuming a 14.7:1 mass ratio of air to fuel, I come up with 1.51 m^3/minute of air being ingested into the engine.

Quote:
Originally Posted by teoman View Post
Lets assume that i am cruising at 2000 rpm with my 3.7L engine.
I do not have a turbo and i am assuming volumetric efficiency of 100. To redo my calculations yourself you can use this site that calculates airflow, and you can plug in your boost pressures etc... :
Engine Air Amount Calculator

So at 2000 rpm, my engine consumes 4.6m^3 of air per minute.
4.6 is about 3 times that of 1.51. This is because that linked website assumes wide open throttle. That's good for base turbocharger calculations, but bad for calculating part-throttle cruise. Remember, there's a vacuum in the intake manifold, which is necessary for gasoline engines because the vacuum performs the oxygen metering.

Let's go through the rest of the calculations here - I've bolded all the numbers that would change as a result of the revised volumetric flow rate.

Quote:
Originally Posted by teoman View Post
239 * 1.51 = 360.9 calories to heat it up by 1 deg (per minute).

Lets assume that the outside air is at 20 degs C and i want to bring it up to 80 deg C.

60 deg C temp difference so:

21653 calories are needed per minute. ( I have calories so:

Divide that by 540 we get 40.1 grams of water vapor are needed.

...

Just to check feasibility, that would roughly make: 2.40 liters of water per hour.
That makes your water to fuel ratio 2.4/10, or 24%. Seems much better than 70%.
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Old 03-20-2017, 11:13 AM   #10 (permalink)
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Thanks a lot. I knew i was goofing up somewhere...

Now how to fool the MAF?

Also is there a separate intake air temperature sensor?

Or should i have the system constantly on and hope that the car uses the O2 sensor to learn?

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