Compressed Air Car: Feasibility & Analysis

[nishat]

hi there,
i am studying the feasibility of compressed air to power a car as my final year project and i need some guidance.

How i proceeded:
(1) I derived equations for the driving force and consequently for the road-load power of a car, with speed as the variable.
(2) I worked backwards using data about power losses in engine and in car transmission which i assumed to be almost constant. I tabulated the indicated power and indicated mean effective pressure inside the cylinder required at different speed
(3) I then calculated the inlet pressures of compressed air required at different cut-off ratio and at different speed if the engine was to operate as a reciprocating piston air motor with 4 cyl in line such that when two pistons are doing the power stroke, the other two are performing the exhaust stroke.

My questions are :
1.Can a conventional car engine be used as a reciprocating air motor, that is, with the same piston-cylinder assembly, piston rings, connecting rod, crankshaft?
2.What about the valves?

 

[chayced]

Oh no not again.
We already have a compressed air car thread, although little out of it may be useful to you since it seemed to verge on perpetual motion at times.
https://www.physicsforums.com/showthread.php?t=310462

To answer what I can.

1. Yes with extensive modifications. May not be worth it to you, since the cost of modifying is probably more expensive than an off the shelf air motor.

2. Complete rework on the valves/camshaft. A regular internal combustion engine has valve strokes that are very different from an air motor. You have to get rid of the compression phase.

Your best bet may be to use a 2 stroke diesel modified for bash valves. These have been used for steam powered setups, but should work just fine with compressed air. Or alternatively you could use existing air motors and avoid the hassle entirely.

One of these on each wheel and I think you would be in buisness.

http://www.grainger.com/Grainger/items/5KB10?Pid=search

 

[nishat]

1. Yes with extensive modifications. May not be worth it to you, since the cost of modifying is probably more expensive than an off the shelf air motor.

2. Complete rework on the valves/camshaft. A regular internal combustion engine has valve strokes that are very different from an air motor. You have to get rid of the compression phase.

Your best bet may be to use a 2 stroke diesel modified for bash valves. These have been used for steam powered setups, but should work just fine with compressed air. Or alternatively you could use existing air motors and avoid the hassle entirely.

Hi,
I understand that it's boring to discuss the same topic, but, thanks for the reply. (i really needed help)

Luckily I am not building one; but i need to discuss these in details in my project.

1.When you mentioned 'extensive modifications', apart from lighter materials and flat piston design etc , can we use the same design of crankshaft, connecting rod. (I could not get much info about reciprocating piston air motor.)

2. If I am right, the valve strokes depend on the profile of the cams. Is it possible to replace the existing cams by new cams designed to allow the valve to open for inlet stroke until cut-off, close for power stroke (expansion), and open again for exhaust stroke? In addition, two pistons will perform the same stroke simultaneously (ex power stroke) while the other two will perform the exhaust stroke.
i have to read more about bash valves.

I read about air motors at wheels, but, do not know much about it. I calculated the input pressure of air to provide the same power output based on the existing I.C engine.

 

[unclejoe]

nishat,

Google "MiniCAT" for all the information you would care for about compressed air motoring.