Air/gas engine hybrid idea
 

I'm planning on taking the back three cylinders in my inline six and running them off of compressed air, the idea is that it would increase low end torque will also allowing me to remove the starter cause one of thoughs cylinders will always be in the power stroke so to start all you have to do is open the compressed air valve. I'm in construction so I have a compressor to maintain compression the only things that come to mind that I'm going to have to do is buy a special camshaft(about $180) cut the back three ports off the intake manifold and manufacture a manifold for the back cylinders, and then get the fittings to adapt the compressor to my jeep and control throttle. Any thoughts on this??

My first though is that you're going to need to use higher pressure air than that typically used for use with air tools, both in order to get useful power out of those cylinders and to be able to store a useful amount of energy. Dive cylinders might do it, if you can figure out a way to control the air at those sort of pressures..

I'm planning on buying a 400psi compressor, it has a 400psi side for curtain tools and a 150psi side for the tools I already have! Do you think that's enough pressure??

I don't think so but maybe.

As a quick first pass assessment, if you assume:

An air tank volume i.e. V1, of 100 liters (26 US gallons)

Adiabatic expansion (no losses), so not realistic.

Between:

Tank pressure, P1 = 400psi = 2775 kPa

and

Atmospheric pressure, P2 = 14.7 psi = 100kPa.

k for air = 1.4.

Using: P1*V1^k = P2*V2^k

Gives V2 =0.714 m^3

Plug that into:

w = [(P1*V1)-(P2*V2)]/(1-k)

Gives work = 417.5 kJ

At a rate of 4kW = 4kJ/s, that will last a little more than 100 seconds. At 40kW, 10 seconds.

You may be thinking about a setup similar to what was done in opal mining zones in Australia, where Beetle engines were repurposed to be used as stationary air compressors for pneumatic tools. 2 cylinders remained working as they were designed to, while 2 others were reconfigured to 2-stroke and used only to compress air. Actually, if I were you I'd rather get a 4-cylinder engine for the Jeep and bolt an air compressor into that.

BTW if you're considering to use pneumatic power to move the vehicle, you should search for that prototypes released recently by Peugeot and Citroën with a pneumatic auxiliary drive as an alternative to the electric auxiliary drive which got mainstream in production hybrids.

How will you power the compressor? I do not have any idea why, but I once figured out how much air an engine needs, wondering about using it in a vacuum or something, and storing enough air to use for combustion was unrealistic. As Occasionally6 demonstrated, air-powering an engine would not really work with tanked air.

I think that cRiPpLe_rOoStEr had an interesting contribution, using an ICE to compress air and the Peugeot and Citroën prototypes.

People often said that if crazy ideas work, then every car manufacturer would be using them.

Except my mother. She is a conspiracy theorist and insists that people have invented far more efficient engines, great hydrogen-cell systems, etc, the oil companies did not like them, and they disappeared. However, one of my professors mentioned a friend that came up with an oil system for cars that would last much longer. He was sued until he went bankrupt and then they bought his patent.

Maybe his system was not so much better. Perhaps he could have proved that it lasted 7,500 miles, while most people tell you to change it every 3,000 miles.

Anyway, I think that there is plenty of room for innovation. Not all ideas are viable, though. Hopefully, our friends here can give you more feedback.

I've done the same; there are not too many truly new ideas :). It might be made to work in drag racing, used like N2O, but dive cylinder type pressures are still required to get a reasonable mass of air.

Using the stored air for supercharging has been tried. There are a couple of SAE papers on it (written in the '50's?).

The initial variant used an air ejector above the carburettor to provide the compressed air. (You've probably seen an air ejector if you've watched an F1 race; they're the short tubes connected to airlines they use to cool the drivers.)

The later version used additional poppet valves in the cylinder head to inject the high pressure air directly into the cylinder, after the normal inlet valve had closed.

The idea was to use a downsized engine and save some fuel when the extra power wasn't being used.

An auxiliary compressor was attached to the engine and a (large) high pressure storage tank installed in the trunk.

I don't know how close you want to get to the same sort of torque your engine can make but using the lower end of peak cylinder pressures during combustion your compressor would need to be able to compress 53000 liters of air a minute to about 290psi,thats at 1500rpm. I don't know what compressor your using but that sounds like a pretty big compressor to me.

Current oil systems allow for 7,500+ miles. I change mine every 8,000, the same time I rotate tires. The 3000 mile mark is a conservative one, usually recommended for vehicles that do mostly city driving. Most people cite that number because oil changes are cheap, its the one thing you do that effects engine longevity the most, and why not use the most conservative interval.

As for the air powered engine, gasoline combustion is going to be more efficient and practical. To produce the amount of air required you would need an on board compressor that uses electricity or gas. If you go electric you need to buy batteries, find a way to charge them, etc. Using gas to power a compressor to replace gas is counter intuitive, as gas combustion would be more efficient. Electricity still costs money, and I tend to believe that powering an air compressor to power the engine, rather than using an electric motor, is less efficient therefore will just be more trouble than it's worth.

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

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

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.

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?

You can use equations for BMEP.
 

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

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.

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.

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.

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

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

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/

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???

That is mean (average) pressure. You might bleed your air into the cylinder to maintain the pressure constant as the piston descends and that would be (ideally at least) a valid condition, as distinct from a simplification.

You might consider though, that a constant pressure expansion extracts less of the energy from the gas than does adding all the gas you are going to expand (with the same internal energy and at a higher pressure) at TDC.

I would encourage you to have a play with some Pressure:Volume (PV) plots to see the effects of different ways of doing things. You don't need calculus, just basic high school math, to determine the areas if you plot on graph paper and count the squares between the boundary lines. The units matter less for the insight than the do the relative magnitudes. Maybe buy or borrow an introductory text on thermodynamics. It's all been done before, in various forms.

There is still the fundamental problem of there not being much energy contained in the stored air. The standard heating value of just one kg (~1.3 liters) of gasoline is 43MJ. That compares with the 420kJ available (assuming that is somewhat close) in the 100 liters of air at 450psi.

CO2 might be easier, with lower storage pressure and the ability to be stored at ambient temperatures. Maybe safer and cheaper also. It's quite common to use CO2 to power rams in Robot Wars so maybe you'll find some info. around them.

CO2 has virtually identical thermodynamic properties (at least at the temperatures and pressures likely with this) to N2O, so readily available N2O system parts might be used with CO2.

With a phase change working fluid, like N2 or CO2, there has to be heat available from somewhere to allow the phase change. There are charts around on the web for both materials that will give you the pressures, temperatures and energy required for the phase change across a particular temperature and pressure change. To start:

Psychrometrics - Wikipedia, the free encyclopedia

Temperature

Enthalpy

With what you are looking to do, it might be (theoretically) possible to use the heat in the coolant from the cylinders that are operating as an ICE. You'll need some idea of the power you want to generate (= the mass flow of N2 or CO2 you want to change phase) to assess that.

Multiply the specific heat of vaporization by the mass of N2 (or CO2) you can store and that's you maximum available stored energy (to be extracted from the environment). without even calculating it, I expect it's still much less than the energy in gasoline.

Given an ICE cylinder can be modelled approximately as adiabatic (no heat transfer), I think you may have difficulties in getting sufficient heat to transfer fast enough into your working fluid to generate a useful amount of power.

That's why combustion engines are internal combustion engines. It's not possible to transfer heat fast enough into and out of the working gas to produce useful power so we use combustion to heat the gas, then mass transfer, exchanging the hot working gas for cold, then start again.

I suspect there may also be issues with trying to operate part of the engine very cold and part of it hot (differences in thermal expansion/contraction).

Using the compressed air for supercharging a downsized engine looks better :).

Thanks occasionally6 you reminded me of something important! On the air engines they had it had a really high cr, not that that maters in a air engine but if you look at it you find that the air used to the power gained is pretty high. For example you take a cr of 16-1 at a starting pressure of 15psi at BDC you'll need about 240psi at TDC, which is a mbep of 60 which is also 1/4 the air isn't it?? So if I wanted a mbep of 5 then I'd need 20 psi which then gives a BDC pressure of about 1.25psi. And if you some how had a 32-1 cr engine then for a mbep of 5 you'd need I think 40psi but for that little bit I'd have about 2/3 the torque am I right or am I getting it messed up here???

I think that treating it as adiabatic is a reasonable approximation. If I use the wiki on adiabatic process example again, the result using a 10:1 compression - expansion will be a simple reversal of that - from atmospheric pressure (14.7 psi) resulted in 360 psi at TDC, so I think you may be out with 16:1, 15psi (gauge?) and 240 psi.

You do have to use absolute pressures, rather than gauge pressures for the formulas to work.

The SAE paper covering the 1959 air injection supercharging is 920843 (it was written about much later than 1959). I don't have a reference for the earlier "Ramaire" air ejector work.

In summary:

A S/C 2.7l six replaced 6.1l V8.

Air was stored in 2 x 2l spheres at 3000psi.

The auxiliary poppet valve used to introduce the air used a variable lift mechanism to control the amount of air introduced.

Fuel savings of 18% highway, 9% city were thought possible.

Peak savings were higher:

@ 20 mph, 47% w/o compressor operating, 35% with.

@ 60 mph, 25%, w/o compressor operating, 15% with.

There's probably a page or two around that will do the calcs for you if you plug in the relevant data.

Yep:

http://www.tribology-abc.com/abc/thermodynamics.htm

Inline sixes are inherently balanced, I don't know how the balance is achieved; but you might be messing with that.

The compressor cRiPpLe_rOoStEr mentioned is available from Dunn-Right Incorporated. IMHO you're just starting with the wrong base vehicle.

Also, the best solution would be the Scuderi Split-Cycle engine
http://upload.wikimedia.org/wikipedi...ne_-_Cycle.gif
The technology appears sound, but the company is getting "Tuckered".
Green Car Congress: SEC issues cease-and-desist order against split-cycle engine developer Scuderi Group for violations of Securities Act

That was a long and technical article. I read about the first half. So, Scuderi has a legitimate invention, but they illegally obtained investors?

I guess that they should not have done that...

If they go bankrupt, can someone else purchase the patent?

Hopefully, it would be someone that would actually use it.

It won't change the balance as that's inherent in the arrangement of the pistons and rods on the crank. It can affect the firing frequency, which will affect the impulses acting on the flywheel. Those are reacted by the mass of the engine and car. That's what you feel in an engine with uneven firing intervals.

Disabling either the front or rear 3 cylinders will keep the firing interval - 1-5-3-6-2-4 goes to either 1-3-2 or 5-6-4 - even but it may not be the best solution in terms of distributing heat evenly through the engine, where 3 cylinders are releasing heat and 3 are absorbing heat.

The VW based compressor shows that it can be made to work, at least in being able to compress air. Idle stop-start could also be done.

I think a variation on the Swiss engine, with the 3 working cylinders supercharged, and the valve switching task simplified by the 3 other cylinders acting as the compressor/starter, is practical (if not trivial to implement). It's heavier than using the same cylinders for both compressing and working tasks but no heavier than the engine is now.

They jumped all over Tucker for selling fitted luggage for a car that wasn't shipping. :confused:

The Dunn-Right is a functioning gas engine/compressor sold worldwide since 1987, although the example I saw had the starter turned around so it sat over the engine instead of the transaxle.

It seems reasonable to me to have one installed in a trike with a winch and Snap-on toolbox. Sort of a shop truck.

As for Scuderi they seem to be better at spending millions than producing even one example running in public. For instance they hobbled their development work by creating a proprietary VR4 engine block when they knew the compression cylinders need to be bigger than the ignition cylinders. Quoting here:
So you can't just pirate Scuderi's patents (which expire when?), but you probably could sell a kit of parts that would allow individuals to create their own (Not For Resale :)). The trick part that would make it all work would be a re-indexed roller-bearing crankshaft.

I think if you have to start changing the engine bottom end it gets expensive. It's not too hard to swap a camshaft (was $180 mentioned for the cam?) and arrange some plumbing.

On another topic, I suggested earlier a look at an introductory text on thermodynamics might be useful, forgetting there's a trend towards easily accessible online course material. There is of course more than one but this looks OK to me:

Thermodynamics Graphical Homepage - Urieli - updated 9/10/2013)

Expensive and touchy—detonation, or the rear wheels re-contacting the ground, can re-index the crank on the fly. People TIG weld the parts together and break the welds. In a car with EFI, that keeps the wheels on the ground and isn't drag raced, they should survive.

But as a development platform it would be serviceable and much less expensive than Scuderi's approach. The offset between the compression and ignition cylinder is reported vaguely as somewhere around 15-22°. Once that is locked down, your 3D printed sintered-metal part with integrated roller bearings can be created.

The Dunn-Right website is a mess—parts with no price and price with no parts—but it looks like $340-380 for the basics, $6500 for a complete unit. They claim a redesign at some point:
I've got unlimited long distance phoning, I think I'll give them a call on Monday.

You're getting a bit obtuse there.

If I understand what is being done with the Scuderi principle, they're separating the compression and expansion cycles. With that done, the compression and expansion ratios can be asymmetric.

It's fairly simple, at least in principle, but not really practical to DIY (at least not without a machine shop).

If we accept that the bottom end, including CR, has to remain the same, what can be done and what is the best approach?

Simply disabling 3 cylinders will help fuel economy due to the reduction in pumping loss. You could do that with minimal changes to the engine management (although you might have to increase the idle speed). The penalty is the maximum power output of the engine is less than will be required at times.

The question then is; How do you regain the extra power when it is required? It might be possible, as per stovie's original idea, to convert the 3 "spare" cylinders into an air powered motor. Unfortunately, the extra power available and most critically, the total energy available, is likely to be quite low. (How many hills do you have to climb?)

You could instead, use the 3 "spare" cylinders as a compressor and feed stored (tank) high pressure air into the inlet manifold - I'm thinking air ejector - and supercharge the 3 working cylinders when the extra power is needed. Accurate control of the extra air may be an issue.

It would require engine management changes. I think the Jeep uses a MAP sensor. There are (2 and 3 Bar) MAP sensors around if the engine management can be rewritten (or swapped) to suit.

There may still be insufficient air available, even with pre-charging of the tank(s). I gather that is one reason why the Swiss engine uses a turbocharger. It may just be that most people aren't prepared (nor able) to charge up tanks of air.

Intercooling could be near perfect with sufficient heat exchange (maybe just long pipes between the engine and storage) from the compressed air to the atmosphere. Even better than 100% with expansion occurring in the inlet manifold.

Another couple of thoughts:

If you allow high pressure air into a cylinder that hasn't quite gone past TDC it will spin backwards (for air driven start after stop).

Although the air store may start out at 450 psi (or whatever), the pressure will drop as air is removed from the store i.e. you have to work using pressure somewhat lower than the peak storage pressure. It also means that you cannot extract all the energy from the stored air because you have to set a minimum, working, pressure.

Some ideas might initially sound crazy, but are actually quite smart. The problem is all about marketing.

While on ideas. The Stihl 4-Mix is worth a look. It's a crankcase supercharged 4-stroke, not vastly dissimilar to the Scuderi engine, just using the non-combustion side of a single piston rather than two separate pistons.