TESTS and ANALYZES of RESULTS about MDI TAXI

Translated by Marsupy (on autos.groups.yahoo.com/group/mdiaircar) from www.mdi.lu
(Below is a 2003 file -- MDI has advanced quite a bit since then)

TESTS and ANALYSES of RESULTS about MDI TAXI

Since the beginning of our work, we have been the aim of various attacks concerning capabilities of our vehicles, and particularly in known newspapers as well on Internet, (emanating from some people who, according to their capacity, could make their statements credible) and all and anything was told.

It is time to restore the truth concerning the real capability of range of our cars.

Comparison between the range of the taxi (prototype) and the range of the final car

Tests and analyzes of the results about MDI taxi

Many tests have been done in the traffic with the Citycats taxi prototype. With these tests, we successfully checked that compressed air, as source of energy, was able to run a car in urban cycle. The features of this vehicle are not yet in conformity with the specifications, but the analysis of the test results confirmed the calculations carried out at the time of the dimensioning of the vehicle (volume of the tanks, mechanical systems, etc.).

A comparison between the definition of the prototype taxi and the final car (under development), gives a quite good idea of the performances expected on the standard vehicle.

Main features of the prototype

Length: 3.84 m

Width: 1.72 m

Height: 1.75 m

The mass of this prototype is 1130 kg, against 700 kg for the final vehicle. This difference is due, amongst other things, to the structure of the frame (made of welded steel tubes), to the mass of the tanks (approximately 4 × 70 kg for 4 × 50 liters, 50 cubic decimetres, at 200 bars, 3000 psi), and to various elements borrowed from standard vehicles (gear box, suspensions system...), and from the industrie (regulators, etc...).

Compared to the current prototypes, on the test taxi, the engine is vertically placed at the front.

At present, Citycats are rear wheel drive vehicles and the engine is under the floor at the back of the car.

This architecture allows an energy saving, because the variation of the angle of the axes of transmission (due to the movements of the suspension systems) is weak if we compare it with the variation obtained by turning the wheels (in the case of a front wheel drive vehicle).

The tanks, assembled for the first on road tests, are heavy (steel) and can only contain a maximum pressure of 200 bars (3000 psi). The final vehicles will embark air at 300 bars (4500 psi) in bottles made of carbon fiber rolled up on a thermoplastic liner. It is possible with this technique to obtain tanks whith a mass of 35 kg for 100 liters of air at 300 bars (4500 psi) while respecting the current safety requirements.

The engine is the 08P03.

Suction/compression cylinder: 234 cm³

Volume of chamber: 593 cm³

Expansion/exhaust cylinder: 28 cm³

This engine belongs to series 08. This series involves the studies on separations of the functions (with suction/compression cylinder, external chamber, and expansion/exhaust cylinder). It has a classical rod crank system (without the "stop and go" system of the piston), which penalizes operation. Indeed, with this architecture, the curve of torque appreciably decreases when the engine speed increases, because there is no time to establish the pressures on the piston. To compensate this lack of time, the injection pressures in the engine of the green taxi were increased (between 70 and 120 bars, 1050 and 1800 psi) that reduces considerably the usable volume of air. Moreover, the timing of this engine consumes a lot of energy (approximately 0.8 kg.m).

Other data

It should be also noted that the system allowing to turn off the engine when the vehicle does not run is not present on this prototype and that expansion between the tank (at 200 bars, 3000 psi) and the engine is carried out through a classical pressure regulator (expansion from 200 bars, 3000 psi, to the inlet pressure is not rigorously isothermal). The usable volume of air is thus reduced.

The green taxi does not either have the system for energy recovery when braking (pneumatic system allowing to recover approximately 13% of the energy of braking).

Experimental course

The run for the present test was carried out between the site of MDI workshops in Brignoles, FRANCE (Forum Aurélia, route du Val) and the shopping centre of St Jean district.

This course (in urban cycle), return trip, is 6.44 km long and we added three rides around buildings of MDI that gives us a total distance of 7.22 km.

Comparison between the range of the prototype taxi and the range of the final car

Considered distance	Prototype features	Final vehicle features	Correction factor	Corrected distance
Influence of mass and mechanical systems
7.22	Gross weight 1226.5 kg. No energy recovery when braking. Engine not turned off when the vehicle is at a stop. Timing uses a lot of energy => power consumed at idle speed.	Gross weight 820 kg. Energy recovery when braking (13.7 %). Engine turned off when the vehicle is at a stop. Variable lift timing ? ("distribution à levée variable ") with low fuel consumption.	1.96	14.15
Influence of usable volume of air
14.15	Steel tanks with low volume and low pressure (200 liters – 130 bars, 1950 psi, usable pressure). Classical pressure regulator. Classical rod crank system (limiting the usable volume of air because increasing injection pressure from 70 to 120 bars, 1050 to 1800 psi).	Tanks made of carbon fiber filament winding (340 liters - 270 bars, 4050 psi, usable pressure). Three stages expansion handled by controlled timing. Rod crank system with stopping of the piston at the top dead centre (PMH, " Point Mort Haut ", in french) allowing to decrease the injection pressure (30 bars, 450 psi).	3.90	55.18
Power consumption of the timing (valve gear drive)
55.18	Sealing of the timing by friction on revolving elements. Absorbed torque to drive the timing is about 0.78 kgm.	Classical type sealing of timing with reduction of frictions by using rollers.	2.51	138.50
Three stages expansion with ambient thermal energy recovery
138.50	Single expansion on a classical rod crank system. Classical pressure regulator.	Three stages expansion that allows to almost reach the isotherm.	1.38	191.10
It should be noted that this estimate of the range of the standard vehicle does not take into account the fact that the taxi has classical tires that could be replaced by green tires, making the range progress from 4 to 5%, and the fact that the car became a rear wheel drive vehicle was not considered. This brings us to the 200 km announced at the beginning of development. To improve range, the embarked volume of air can be increased considerably (by modifying the diameter of the tanks as well as the pressure of use), without challenging the viability of the concept (cost and ease of use, pollution, etc...)
Possible increase of usable pressure and volume of air
191.10	We can easily modify the volume of air in the tanks and increase it to 400 liters. For the calculation of the correction factor, we took into account the increase of volume and the increase of mass (+ 50 kg in the calculation of the required power for the course in urban cycle).		1.11	212.98
212.98	If we increase the pressure of these 400 liters to 350 bars (5250 psi), we obtain an overload of 100 kg (average of the mass of air added + additional carbon fiber mass for the tanks)		1.26	242.10