Why data about fuel consumption, driven by car manufacturers do not coincide with actual performance? This frequent question is doctor of technical Sciences Klaus Rohde-Brandenburger, engineer of the concern "Volkswagen".
Conditions for measurements on the NEFZ cycle are difficult to reproduce in reality. The tests are conducted at a comfortable temperature of 20 ° C, with the energy users turned off and without reference to the constantly changing road situation. AND NOT IN EUROPE, and not only for the measurement of fuel consumption and CO2 emissions, use the so-called new European test cycle NEFZ (der neue europäische Fahr-Zyklus). It consists of an urban area of 4 km and a 7 km extra-urban section, for each of which fuel consumption is calculated separately. According to the data received, the total is calculated for the entire 11-kilometer distance. Three of these costs-urban, extra-urban and mixed-are given in the certification documents of the car, they are also published in advertising booklets and catalogs as information for potential buyers. The fuel flow rate in the mixed cycle is used in Europe for the calculation of the transport tax. It is probably because it is most often placed in the foreground and the other two values, equally important, are printed in fine print or are ignored. Although it is precisely the range between urban and extra-urban costs for consumers, it demonstrates how much the fuel appetite depends on the operating environment. This is often overlooked by even technically competent automotive publications, comparing the test results with the costs of the mixed cycle only. There is no doubt that there is a discrepancy between the manufacturer's official data on fuel consumption and operational values. The main reason is that the actual expenditure is often compared to the NEFZ mixed cycle. For example, take the data obtained from the NEFZ "Volkswagen-Golf" methodology with a 1.4 liter 122-strong engine. Average fuel consumption in the NEFZ cycle of the Volkswagen Golf car (1.4 litres, 90 kW/ 122 litres). , 6-speed mechanics). All schemas are opened in full size by click. In the mixed cycle, it pulls out of the tank 6.2 litres/100 km, 32 per cent less than in urban (8.2 l) and 18 per cent more than on the road (5.1 l/100 km). It is solid, but in this range, most of the values recorded by the owners are in real use. In addition, NEFZ shows a good demonstration of how the fuel flow is affected by the length of the route. If the entire 11-km Golf segment burns a little more than 6 litres per 100, then the first 2 km, when the engine is not warmed up, the amount spent is almost double the amount spent. Conclusion: for short trips, the cost may exceed even the highest declared indicator-urban. COMPILING THE PRACTICE OF EQUITALIZATION OF THE three official values given by the manufacturer, with the actual fuel consumption recorded by me. Volkswagen-Polo 1.4 TDI (2004 model year) has passed a total of 9,700 km. The cost of the combined cycle for this model is 4.5 l/100 km, and the average measured by me for all 633 trips is 5.1 l/100 km, that is only 13% more. This difference is negligible, given the number of factors that fuel the fuel appetite. For example, what is the impact of ambient temperature? To investigate this, I have long been recording the thermometer and meter readings for each trip to work. On different cars, petrol and diesel, but adhering to a uniform driving style. For temperatures from 1 to 5 ° C, the reference 10-kilometer point is not different from that of the NEFZ combined cycle. In addition, the curves for diesel and petrol variants match. But the main conclusion is that the reduction of the outside temperature of 20 ° C results in an increase in fuel consumption by an average of 20 per cent. There is no doubt that not only in the warm-up engine, but also the greasing lubrication in the gearbox, the differential, bearings, the increased tyre rolling resistance and the worst aerodynamics due to the high air density at low temperatures. Fuel costs "Volkswagen-Polo 1.4 TDI", as compared to the NEFZ cycle test data. The nature of the drive is even more economical. In the measurements, even short-term, forced acceleration in reduced transmission significantly increased the flow rate than the fall in temperature, the results of these trains were rendered absolutely unsuitable for analysis. Therefore, I decided to hold another series of measurements-with economic management of the car and with the emphasis on sports. The difference in the 10 km checkpoint was about 25 per cent. In your mind-only the temperature and temperament of the driver are able to increase the spending by almost half! Naturally, the tests carried out in the greenhouse conditions on the rollers do not, in most cases, repeat real trips. Therefore, the indicators specified in the manufacturer's catalogue will differ from the operational fuel consumption. Regardless of the manner in which the tests were conducted. In real terms, fuel consumption is affected by many factors. Therefore, the figures vary even by half in different circumstances. The leading German edition of Auto, Motor & Sport compared the own measurements of petrol and diesel oil "foil" with fuel costs specified by the manufacturer. The log indicates three flow rates in each test. In addition to the average test, records the minimum measured by its own method and the maximum test achieved during the test. The range of these values is close to the range of "urban-urban", which proves once again that NEFZ provides consumers with reliable and useful data on fuel consumption. Klaus Rhoda-Brandenburger: "In real life, for many reasons, there is inevitably a difference in fuel consumption, so the theory will always go with practice." By reviewing the periodic, I noticed the difference in the costs between the test results of the different journals. For the same models, it is up to 27%. However, most of the test values are stacked between urban and extra-urban. Another source of real economy is the Internet. I found the costs presented by the 20 owners of Golf 1.4 TSI (90 kW and the manual box), who had gone for a period of at least 10,000 km for the year 2008. The values range from 6.2 to 8.3 l/100 km and are thus 34 per cent different. The average value is 7.08 l/100 km, which is only 12% greater than the cost for the combined cycle. Only the verification of the fuel consumption in the NEFZ roller test bench shall be physically credible, subject to the conditions prescribed for standard certification tests. The manufacturer's cost data is only a guideline that enables customers to compare them with other car models. WHAT DO YOU DO? Average fuel consumption in daily life is affected: route length; speed; gearshift mode; frequency and intensity of accelerations and braking; ambient air temperature; energyfree users (climate installation, entertainment systems, electric heaters); additional load (passengers, luggage, roof, trailer); density and speed of traffic.