Air/gas engine hybrid idea

[Occasionally6]

Originally Posted by stovie

Ok using the bmep method I only need 68psi to equal the same torque my engine has now.

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.

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???

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 .

[stovie]

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???

[Occasionally6]

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

[freebeard]

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... Any thoughts on this??

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

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

[Xist]

Originally Posted by freebeard

Also, the best solution would be the Scuderi Split-Cycle engine

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.

[Occasionally6]

Originally Posted by freebeard

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

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.

[freebeard]

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

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:

The upright motors cannot just change strokes and bores. The block is fixed and has to maintain deck heights. To change strokes means you have to change rod lenghts, piston pin heights.

For the horizontally opposed motor, you can change any stroke, bore and lenght of motor...regardless of where the pin height is. The variations are almost endless. This is the beauty of the Aircooled VW.

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.

[Occasionally6]

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)

[freebeard]

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:

This challenge sparked the creation of the new generation of "Volks-Air"
compressors. These compressors, operating with a new concept, not only are
cheaper to build and produce more air but offer numerous other advantages.
These self-governing, auto-unloading units run with virtually no vibration.
Their lightweight design and high speed capability make them very efficient.

I've got unlimited long distance phoning, I think I'll give them a call on Monday.

[Occasionally6]

Originally Posted by freebeard

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.

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.