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Diesel exhaust gases cause serious diseases, while any repair of a compression-ignition engine is rather very expensive. LPG may be the real alternative – it cleans the exhaust gases, reduces costs and simply "tames" Diesel engines. This has been confirmed in 100.000 test travel distance by AC S.A.

The experience gained so far clearly shows that there is no point to enter the Diesel market, particularly if there is a petrol alternative that can be easily converted to LPG.  Thanks to an innovative approach and capacities provided by the Development and Research Centre

at the Polish company AC S.A., this stereotype was overcome - a reliable autogas system dedicated for Diesel engines was developed. To finally confirm the significance of this product, the STAG-Diesel was tested by the manufacturer over the driving distance of 100.000 km before launching into the market. The test assumptions and procedure were as follows:

There were mixed drive cycles, but extra urban drives prevailed (80% of driving distance vs. 20% of urban drives). Every 15.000 km the car (2012 Toyota Hilux pick-up, 2.5 Euro 5 engine, 144 HP) turned aside from the route to a laboratory to measure (in the presence of an expert) the following parameters and elements:

• turbocharging pressure;
• cylinder liners (endoscopic examination);
• power and torque momentum;
• gas injector efficiency (AC W01);
• reducer operating stability (AC W01);
• fuel consumption (Diesel oil and autogas).

Warranty inspections of the test car were carried out at an authorized service centre, and the test results were summarized by overall engine tests, and the results were described in a comprehensive and detailed report.

One of the most important parameter checked after the test was the valve clearance measurement. The limits specified by the manufacturer are as follows: 0.35-0.45 mm for exhaust valves and 0.2-0.3 mm for inlet valves. However, the measured values were: 0.36-0.38 mm and 0.21 mm correspondingly, thus met the requirements, and no clearance adjustments were required.  The progression of clearance reduction was also minimal - an inspection after the 1000 km test showed clearances at the level of 0.38-0.39 mm for exhaust valves and 0.23-0.24 mm for inlet valves. The engine power after testing on engine chassis test bench was 133 HP vs. 136 HP after the first 1000 km.

But what was the performance of autogas installation components? The injectors showed an excellent repeatability - each of four remained open for 2.22 to 2.25 ms (initially, at the beginning of the test this ranged from 2.39 to 2.45 ms, so the flow rate dropped from 55 to 51 l/h, that is by 7.3-8.9%), and closed for 1.17-1.21 ms (compared to 1.29-1.35 ms after 1000 km), thus they not only work very quickly, but are also uniformly wearing and fuel dosing.

For gas-diesel the key question is fuel (in fact, fuels) consumption and related savings. AC S.A. tested their solution in a series of various vehicles (passenger cars, pick-up, SUVs, delivery vans, and even farm tractors), combining diesel fuel with LPG or CNG, thus reducing fuel costs by 7-29% for autogas (the least in Seat Altei and Fiat Ducato 3.0, the most in Mitsubishi Pajero 3.2), and by 16-23% for methane. The tested Hilux showed savings of 13% in average over the distance of 100,000 km, changing average consumption of Diesel oil alone from 10.5 l/100 km to  6.1 l Diesel oil and 6 l LPG per 100 km. With today prices this means the cost of travelling 100 km by more than 16%. But there are fuel costs only that could be enlarged by savings resulting from lower wear rate of the engine and its subassemblies, that cannot be neglected, especially in Diesel engines, although it is difficult to estimate it.

One may say that 16% cannot be considered as savings! But during a year this amount is noticeable for the car user. It should be remembered that, normally, commercial vehicles travel much  longer distances than passenger cars, thus the trip distance of 100.000 km can take not 7-8 years as for a car, but 3-4 years or less. And none of owners of vehicle fleet cannot say that operating costs are unimportant! Especially, when the costs are multiplied by the number of vehicles they use. The long-distance test performed at AC S.A. has indicated that there is no problem at all both with failure-free operation of diesel-gas system and the condition of the engine.  STAG-Diesel works!