The conditions for measurements on running drums using the NEFZ cycle are rather difficult to reproduce in real conditions. After all, tests are carried out at a comfortable temperature of 20 ° C, with energy consumers turned off and without reference to a constantly changing traffic situation
The conditions for measurements on running drums using the NEFZ cycle are rather difficult to reproduce in real conditions. After all, tests are carried out at a comfortable temperature of 20 ° C, with energy consumers turned off and without reference to a constantly changing traffic situation. The conditions for measurements on running drums using the NEFZ cycle are rather difficult to reproduce in real conditions. After all, tests are carried out at a comfortable temperature of 20 ° C, with energy consumers turned off and without reference to a constantly changing traffic situation.
SEPARATE AND DO NOT MIX
In Europe, and not only, the so-called new European test cycle NEFZ (der neue europäische Fahr-Zyklus) is used to measure fuel consumption and CO2 emissions. It consists of a 4 km urban part and a 7 km suburban section, for each of which fuel consumption is calculated separately. According to the data obtained, the total indicator for the entire 11-kilometer distance is calculated. These three values of consumption - urban, suburban 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 combined fuel consumption rate is used in Europe to calculate the transport tax. Perhaps that is why it is most often brought to the fore, and two other values, no less important, are printed in small print or completely ignored. Although the range between city and suburban expenses is much more informative for consumers: it clearly demonstrates how much the car's fuel appetite depends on operating conditions. And even technically competent automotive publications often forget about this, comparing the results obtained during the tests only with the costs in the combined cycle.
There is no doubt a discrepancy between the manufacturer’s official data on fuel consumption and operating values. The main reason is that real consumption is often compared only with the NEFZ mixed cycle rate.
For example, take the data obtained during the tests according to the NEFZ Volkswagen Golf method with a 1.4-liter 122-horsepower engine.
Average fuel consumption in the NEFZ cycle of the Volkswagen Golf car (1.4 l, 90 kW / 122 hp, 6-speed manual)
Average fuel consumption in the NEFZ cycle of the Volkswagen Golf car (1.4 l, 90 kW / 122 hp, 6-speed manual). Average fuel consumption in the NEFZ cycle of the Volkswagen Golf car (1.4 l, 90 kW / 122 hp, 6-speed manual).
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In the combined cycle, it draws 6.2 l / 100 km from the tank - 32% less than in the city (8.2 l), and 18% more than on the highway (5.1 l / 100 km). The spread is solid, but most of the values recorded by the owners in real use fall into this range. In addition, NEFZ perfectly demonstrates how the route length affects fuel consumption. If the Golf burns a little more than 6 liters per hundred over the entire 11-kilometer stretch, then in the first 2 kilometers, when the engine has not yet warmed up, the amount of spent fuel is almost double. Conclusion: for short trips, the consumption can exceed even the highest declared indicator - city.
I CONFIRM PRACTICE
Compare the three official values indicated by the manufacturer with the actual fuel consumption recorded by me. Volkswagen Polo 1.4 TDI (2004 model year) covered a total of 9, 700 km. The consumption in 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 when you consider how many factors fuel appetite depends on. For example, how does ambient temperature affect? To investigate this, for a long time I recorded the readings of the thermometer and flow meter for every trip to work. And on different cars, gasoline and diesel, but adhering to a single driving style.
At temperatures from 1 to 5 ° C, the flow rate at the control 10-km point does not differ from the mixed cycle index obtained by the NEFZ method. In addition, the curves for diesel and gasoline modifications coincided. But the most important conclusion: lowering the outside temperature by 20 ° C leads to an increase in fuel consumption by an average of 20%. Of course, the reason is not only in the cold engine, but also in the thickening grease in the gearbox, differential, bearings, increased tire rolling resistance and worse aerodynamics due to the increased air density at low temperatures.
Volkswagen-Polo 1.4 TDI fuel consumption, obtained in real conditions, in comparison with the test data for the NEFZ cycle
Volkswagen-Polo 1.4 TDI fuel consumption, obtained in real conditions, in comparison with the test data for the NEFZ cycle. Volkswagen-Polo 1.4 TDI fuel consumption, obtained in real conditions, in comparison with the test data for the NEFZ cycle.
Even more noticeable on the economy affects the nature of the ride. During measurements, even short-term forced acceleration in lower gear increased consumption much more than temperature drop - the results of such rides were absolutely unsuitable for analysis. Therefore, I decided to conduct another series of measurements - with economical driving and with emphasis on sports. The difference in the 10-kilometer checkpoint was about 25%.
Think about it - only the temperature and temperament of the driver can increase consumption by almost half! Naturally, tests conducted in greenhouse conditions on running drums in most cases do not repeat real trips. Therefore, the indicators indicated in the manufacturer’s catalog will differ from the operational fuel consumption. Moreover, regardless of the methodology by which the tests were conducted.
Under real operating conditions, many factors affect fuel consumption. Therefore, indicators in different conditions can even differ by half.
EVIDENCE FROM
The leading German publication Auto, Motor & Sport compared its own measurements of gasoline and diesel "Volkswagen" with fuel consumption indicated by the manufacturer. Moreover, the journal indicates in each test three indicators of consumption. In addition to the averaged test one, it fixes the minimum, measured by its own method, and the maximum, obtained during the test. The scatter of these values is close to the urban-suburban range, and this once again proves that NEFZ gives the consumer quite reliable and useful data on fuel consumption.
Klaus Rode Brandenburger
Klaus Rode-Brandenburger:
“In actual operation, for many reasons, a difference in fuel consumption inevitably arises, so the theory will always diverge from practice.”
After reviewing the periodicals, I noticed the difference in costs between the results of test drives of various magazines. For the same models, it reaches 27%. Moreover, most of the test values fit into the gap between urban consumption and suburban.
Another source of real indicators of profitability is the Internet. Then I found the expenses presented by the twenty owners of the Golf 1.4 TSI (90 kW and manual), who traveled at least 10, 000 km in 2008. The indicators range from 6.2 to 8.3 l / 100 km and, thus, differ by 34%. The average value is 7.08 l / 100 km, which is only 12% more than the flow rate for the combined cycle.
Only verification of fuel consumption at a roller test bench within the framework of NEFZ in compliance with the conditions prescribed for type certification tests can be physically reliable. Manufacturer data on consumption are just a guideline, allowing customers to compare them with indicators for other car models.
