Air/gas engine hybrid idea

[stovie]

I saw this show on tv where they were talking about compressed air cars possibly coming to America in a couple years. They had a 1litre engine that could go 800-1000 miles on a full tank of air. The tank had 3500 cubic feet of air compressed down to 890psi. What I'm trying to do is run half my cylinders off of compressed air to hopefully allow better fuel economy(half the cylinders running on compressed air=less fuel burned), allow for easier eoc, and possibly more torque down low. I want to get a compressor that runs to 500psi(I know I said 400psi earlier but I just found out it was upgraded), and also put four 6 inch diameter by 54 inch long storage tanks under the jeep. I'm in construction so ill always have it plugged in at the job. I'm also planning on having the pressure constant so say I have 15 psi on my 3.88 inch pistons, that's a constant down force of 58.2 pounds is it not?? And if I remember correctly at 15 psi 450 psi equals 30 times the air

[JRMichler]

The fundamental problem with any compressed air vehicle is the inefficiency. A one hp industrial air motor needs about 4 hp of air compressor to run it. That's because compressing air makes it hot, and expanding air in a motor makes it cold.

[Xist]

Originally Posted by euromodder

Oil technology has evolved a bit.

Maybe it's time for the US to get along a bit , and change to a more realistic oil change interval ?
Yes, you can ...

The minimum we have in Europe on current cars is 15000 km - 9500 miles.
20 to 30000 km is quite normal here - that's 12500 to 19000 miles

My 1987 Honda Prelude needed a change every 7,500 miles, according to the manual, but everybody shouted that it was wrong and I was ruining my car for even thinking about it.

Honda does not know what they are doing?

[RustyLugNut]

Originally Posted by stovie

I saw this show on tv where they were talking about compressed air cars possibly coming to America in a couple years. They had a 1litre engine that could go 800-1000 miles on a full tank of air. The tank had 3500 cubic feet of air compressed down to 890psi. What I'm trying to do is run half my cylinders off of compressed air to hopefully allow better fuel economy(half the cylinders running on compressed air=less fuel burned), allow for easier eoc, and possibly more torque down low. I want to get a compressor that runs to 500psi(I know I said 400psi earlier but I just found out it was upgraded), and also put four 6 inch diameter by 54 inch long storage tanks under the jeep. I'm in construction so ill always have it plugged in at the job. I'm also planning on having the pressure constant so say I have 15 psi on my 3.88 inch pistons, that's a constant down force of 58.2 pounds is it not?? And if I remember correctly at 15 psi 450 psi equals 30 times the air

Brake Mean Effective Pressure (BMEP). With some manipulation you can calculate an approximate power output for a constant pressure above your pistons.

Here is a good discussion that uses algebraic manipulation rather than the standard calculus based derivation.

Brake Mean Effective Pressure (BMEP): The Performance Yardstick

[Occasionally6]

Originally Posted by JRMichler

The fundamental problem with any compressed air vehicle is the inefficiency. A one hp industrial air motor needs about 4 hp of air compressor to run it. That's because compressing air makes it hot, and expanding air in a motor makes it cold.

That's part of it. The amount of energy it is possible to store is the other. My previous post assumed very ideal "conditions" as a simplified feasibility calculation and even that shows that there's not a lot of energy to had from a reasonable tank volume.

Originally Posted by RustyLugNut

Brake Mean Effective Pressure (BMEP). With some manipulation you can calculate an approximate power output for a constant pressure above your pistons.

Here is a good discussion that uses algebraic manipulation rather than the standard calculus based derivation.

Brake Mean Effective Pressure (BMEP): The Performance Yardstick

The Wikipaedia page on Adiabatic Processes shows a worked example of a compression process that uses very similar conditions to what is being proposed; 362psi, 10:1 CR, 1 liter swept volume. Being adiabatic, it's reversible, so using 362 (~400psi, even 500psi) will only allow a similar power output to that required to compress the air in the 4-stroke cycle. That's much less than is released after combustion.

A compressed air car might use regeneration during braking, which will extend the range a bit. It helps a lot to use a small engine (at least on paper), whether it's air powered or supercharged using compressed air.

Exploring the supercharging idea further. If you converted half the cylinders into an air compressor (and maybe that should be every second cylinder, rather than the front or rear 3 - have to think about that), maybe only compressing at light engine load or on decel., you could then work the other 3 harder and reduce light load pumping losses. The compressed air is then available for supercharging when higher power is required.

The compressed air could be cooled to near ambient i.e. near perfect intercooling.

[Occasionally6]

Originally Posted by stovie

I'm also planning on having the pressure constant so say I have 15 psi on my 3.88 inch pistons, that's a constant down force of 58.2 pounds is it not?? And if I remember correctly at 15 psi 450 psi equals 30 times the air

Extending that reasoning (and I'm not sure it's correct), with (say) a 4" (= 1/3 foot) stroke, that's 58.2/3 = 19.4 ft.lbs of work. At 1500rpm and x 3 cylinders that's 18HP.

With a total stored volume of 96 liters, at 450psi and assuming it does go to 30 times that at 15psi, that's 2880l. In a 2.0l air motor, that's 1440 revolutions (assuming 100% volumetric efficiency). If you ran it at a constant (or average) 1500 rpm that's a little less than 1 minute of operation. At 18HP.

There's room for some exploration of the idea of using compressed air but not to run a motor directly with that kind of pressure.

[user removed]

I had an Austin Healey Sprite that had two burnt valves with practically no compression on two of four cylinders. Absolutely gutless running on two cylinders.

I would do a whole lot or research on this proposed desgin before I started hacking up a decent vehicle. To equal the pressure created by combustion you will need about 7 times the compression pressure, 12-1400 PSI would empty a 3000 PSI CO2 bottle in a very short time.

regards
Mech

[user removed]

Also remember, if you compress air above the cranking compression of a diesel engine (above 400 PSI) you risk auto ignition of any lubricant vapor in a closed chamber, since you have just created a diesel engine.

regards
Mech

[Occasionally6]

Re supercharging, there truly is little that hasn't been tried before:

Supercharger Air Hybrid Vehicle

and this:

http://speedzzter.blogspot.com.au/20...ercharger.html

http://wardsauto.com/ar/compressed_air_engines_090223

http://www.idsc.ethz.ch/Research_Guz...ic_Powertrain/

[stovie]

Ok using the bmep method I only need 68psi to equal the same torque my engine has now. I was also thinking of using liquid nitrogen under pressure as the compressed air part. From what I've read liquid nitrogen will expand from one cubic mm to one cubic meter, there's suppose to be 1000 cubic mm to a liter of liquid nitrogen so I believe that means it has 27,000cf and I found one liter of it for $2 the only other problems I can think of at that point is the pressure, the temperature it will be at and the cost of tanks that can withstand that pressure!any more ideas???