Calculations on the air motor of Mdi: figures finally!

[Christophe]

We were finally able to recover (failing to do it ourselves ...) precise calculations on the famous air car of MDI. These calculations were made in 2003 by the École des Mines de Paris in the energy lab. She is mentioned in the following documentary: https://www.econologie.com/la-voiture-a- ... -3965.html

You can download the full reports here:

https://www.econologie.com/telechargemen ... nes-paris/
https://www.econologie.com/telechargemen ... nes-paris/



Here is the first information from this report:

As an indication, consider 340 l of air initially at a pressure of 300 bar, which expand to atmospheric pressure, P = 1 bar.

The work provided, within the framework of the ideal gas hypothesis is:
For adiabatic relaxation: 20.5 MJ
For a polytropic expansion (k = 1.2): 31.3 MJ
For isothermal relaxation: 58.2 MJ

1 L of diesel fuel contains approximately 10 kWh or 36 MJ
The efficiency of a heat engine is around 0.3 (30%)
1 L of diesel fuel will therefore provide 36 * 0.3 = 10.7 MJ mechanical.

The 340L and 300 bar tank therefore contains the equivalent, at best (100% engine efficiency mdi (!!) on an isothermal expansion) of 58.2 / 10.7 = 5,4 L of fuel! The reality must be between 2 and 3 Liters "diesel equivalent" taking into account the real performance of the engine!

Thus, in order to optimize the amount of work provided by a trigger, it is essential to perform a trigger close to an isothermal trigger. This is why, the concept of a stepped expansion is interesting, characterized by a reheating of the gas (the temperature of which dropped during the expansion) between the expansion stages.

The rest in the doc ...

In short I invite all those who are interested in the engines, near or far to read the doc: air motor calculations

[Superform]

After reading this pdf ...

well i go back to code

we will have to wait a little longer to see these vehicles circulating, in my opinion ...

[Remundo]

They don't lack air at Mdi

More seriously, if there is the equivalent of 4L of gasoline, that is really "short". There's plenty to fall for even in town

[Capt_Maloche]

I resume the message sent in MP to Christophe:

AH yes, that's right:
I knew that there were exchangers on the ambient air

Thus, the efficiency of the isentropic expansion in each of the stages is fixed at 85%, the losses by leakage in the circuits, at the entry of each stage are fixed at 2% (figure probably lower than the real percentage of loss), and the efficiency of the exchangers at 50%.

As indicated above, in table 5, the autonomy of the MDI CAT in the urban cycle would only be 47 km, the maximum value because we have not yet taken into account the consumption of accessories.

7 CONCLUSION
We were able to show here that the autonomy of the MDI CAT was estimated at around forty kilometers, when we consider its operation in urban areas, and the staged relaxation system as we simulated it.
And it is precisely for this type of route that this vehicle is intended.
This autonomy is low, and is subject to the influence of important parameters such as the outside air temperature where the consumption of accessories.
Indeed, in winter, at night, or / and in the rain (operation of the windshield wipers and headlights), autonomy is likely to drop below the 40 km threshold.
We therefore think that the addition of a burner system, powered by diesel (and not by electricity which would further degrade autonomy), is to be considered.

Quote:
Finally it would be interesting to work on a bi-energy engine, operating with compressed air only in urban areas.

It is therefore the autonomy of 2L of fuel which is offered with a charge of 5:30

So 5h30 of charge for 40km of autonomy ... what power already the compressor? What does it cost at the price of km?

[chatelot16]

you understood everything: compressed air and an even heavier means of energy storage than good old lead-acid batteries

compressed air can still be used for something: making hybrid vehicles: for a hybrid it is useless to put a battery too heavy to have a good autonomy: it would be enough of a very small battery of capacity just sufficient to recover the braking energy, and restart the car when starting: it is not possible with a battery: too short a charge or discharge time would quickly kill it

a compressed air tank does not wear out regardless of the filling or emptying speed: it is therefore very good for recovering braking energy: even better the same piston could serve as a braking compressor, the air motor when starting and heat engine when there is no more air

[nlc]

After reading this pdf ...

well i go back to code

we will have to wait a little longer to see these vehicles circulating, in my opinion ...

What are you coding?

[Superform]

It's a secret, you will know everything! ...

but later

[Christophe]

compressed air can still be used for something: making hybrid vehicles: for a hybrid it is useless to put a battery too heavy to have a good autonomy: it would be enough of a very small battery of capacity just sufficient to recover the braking energy, and restart the car when starting: it is not possible with a battery: too short a charge or discharge time would quickly kill it

Exactly although I am not sure that the air is advantageous compared to a hydraulic fluid. Like oil for example.

One of my econological engineering school exercises (rare!) Concerning well worn Polish buses that the town hall could not replace.

They therefore worked on an "other solution" and finally mounted a hydraulic braking regeneration system: thanks to a "beast" hydraulic motor-pump mounted (probably I'm not sure, the exercise was not too detailed) between the engine and the gearbox.

I believe (it's been almost 10 years) that the performances were as follows: + 30% performance at acceleration and -20 to 30% consumption, cost less than 5000 € per bus (compare with a new bus that would have the same performances: more than 100 €)!

The Poles did it 15 years ago ... are we waiting to generalize the system on ALL vehicles (at least say heavy goods vehicles)? The peakoil? We are really too stupid yeah! It's funny this habit of always doing everything in an emergency ...

Finally it would be interesting to work on a bi-energy engine, operating with compressed air only in urban areas.

Well, that was Mdi's idea in recent years ...

[nlc]

The oil is not compressible, I do not see well how one can store enrgie with oil

[Christophe]

The goal is to store energy only 2 or 3 brakes (maybe even one reminds me more) to help the next re-acceleration: no more!

A few hundred (tens?) Of kJ of storage is therefore sufficient (nothing to do with the 300L at 300 bars which store 30 MJ).

I think there was some kind of air or neutral gas expansion "tank" on the line, this is really a long way off but I think we could find some information (patents) on the question .. .