Skoda Praktik diesel-gas - dual practicality

© gazeo.comThe Praktik's cargo area's floor is flat and even. Or rather would be were it not for the CNG tank. Unfortunately, these do not come in toroidal shape

Calibration
Once the gas system was activated, the engine's parameters were virtually the same as on diesel alone, which was confirmed by our dyno tests. A diesel-gas blending system can be tuned to give a power and torque boost, but this is not the case here – the one in the Praktik is there to cut down the fuel costs as much as it can by replacing as much diesel with CNG as technically possible. In fact, boosting power and torque could mean boosting economy, too, but then it depends more on the driver's technique, who uses less fuel by applying less pressure to the accelerator pedal (while still achieving the same dynamic effect, because the power is higher). But since drivers may be tempted to make use of the extra driving force at the cost of economy, the Praktik's system does not offer a boost.

General impressions
The 90-PS engine makes the Praktik quite a lively car, even though engine flexibility left something to be desired (for a diesel engine) – the motor needed relatively high RPM to show proper signs of life. However, this was only visible in city driving and was gone instantly once the car entered a motorway/highway. Driving at top allowed speeds was no problem at all.

The temperature threshold for the engine to switch to CNG power was very low – just 5° C. Even though we drove the car in sub-zero temperature conditions, it would switch to CNG very quickly after the start-up and the switchover was always accompanied by the unmistakeable sound of the opening electrovalve on the tank. Since the cargo area was only separated from the cabin by a wire-net screen, the sound was easily audible and precisely indicated the moment of switchover.

© gazeo.comSeeing a diesel car at a CNG station is not an everyday opportunity

And while we are talking of sounds: when the bonnet was up, the I-plus injectors were quite easy to hear (particularly at higher RPM), especially since they are loud by nature. However, the Praktik's diesel engine is rather harsh and noisy in its own right, so it drowned out the sound of the injectors and hardly any of it could be heard from within the cabin.

Fuel consumption and economical performance
The distance we covered during our test exceeded 1000 km, most of which were motorways and highways. Even though speeds were high, the car only needed 3,82 l of diesel and 2,27 m³ of CNG per 100 km. If we had used diesel alone, fuel economy figure would have been 6,2 l/100 km. Given the prices of fuels at the end of March 2013, the running costs of the Praktik are reduced by 6,77 zlotys/100 km (from 34,78 zlotys on diesel alone to 28,01 zlotys on diesel/CNG blend). This means the car saves 677 zlotys per 10 thousand km, but since cars like this one usually reach annual mileages between 80-100 thousand km, savings may amount to nearly 7000 zlotys (approx. 1700 euros). Once the DegaMix II hits the market, it is going to be priced at roughly the same level as good gas systems for petrol engines. Assuming that the system costs 5000 zlotys (including conversion), it should pay back after some 80 thousand km of driving, or less than a year. This should appeal to many...

© gazeo.comAdd to that some 10 litres of diesel and you will be able to cover up to 270 km

Saving money is just one aspect, but there is another – additional range. Obviously, when you have two tanks, you will be able to drive more before having to refuel. With 55 litres of diesel and a CNG system on board, the Praktik is able to cover 1440 km on a single tank of diesel (given you refill with CNG every time it runs out before eventually diesel runs out, too, for the amount of CNG in the tank is only good for approx. 530 km of constant driving). If you drove on diesel only, the car's range would be approx. 900 km. More frequent refueling may not be exactly convenient, but fitting 3 CNG tanks is not an option, either, for a delivery van with 3 steel pressure vessels in its cargo space could then hardly deliver anything anymore.

To sum up...
There were times when the running costs of diesels were comparable to those of petrol cars converted to run on LPG/CNG. They are long gone now and diesel owners are forced to seek savings beyond low fuel consumption of their oil burners. Modern diesel-gas systems are here to generate these savings and the new DegaMix is one of them. Not only does it inject gas into the air-fuel mixture, but it can also cut down the diesel dose. For now, this is done on the basis of emulating the diesel fuel pressure sensor signal, but Elpigaz continues developing the system to further boost the gas fuel dose, e. g. by emulating the signal of the accelerator pedal position sensor.