If you go to the car manufacturer website, you will look for the fuel consumption rating on the site then you will realize either JC08 rating [1] or Urban/Extra Urban Cycle rating [2] for the fuel consumption.
So what are JC08 and Urban/ExtraUrban Cycle??
In order to understand those two terms, you should realize the world exhaust emissions standard. It is true that different countries should have different regulations on vehicular exhaust emissions however there are only three major regulations that govern the vehicular exhaust emissions:
- European Emission Standards (EU/ EEA) - the most common
- United States Emission Standards (EPA) - the second most common
- Japanese Emission Standard
Regardless which countries (that have implemented vehicular exhaust emissions regulations), either one of the above standards is the foundation to develop local regulations on vehicular exhaust emissions. A rather easier way for policy makers to do their work is they can just follow either one or all of the standards above by specify that their country recognize this specific standards.
For example, if the country only recognized EU Emission Standards, car manufacturers with EPA standard or Japan Emission Standard are required to bring their car model to perform exhaust emission testing based on EU Emission Standards before the car model can get the type approval/license to travel around that country. This is basically what my industry look like.
In reality, most countries that are lack of profession in this area would just simply recognize these three standards above to allow the automobile industry to runs smoothly since majority of the vehicle were either European made or Japanese made.
Since most cars either European Made or Japanese Made, I would like to focus on EU Standard and the Japanese Standard. Regardless which standards, the exhaust emission test must be conducted in a laboratory environment where the vehicle would be placed on the chassis dynamometer to allow the wheel to rotate in order to simulate the driving condition.
In the test procedure, the testing driver must follow a speed-time graph while driving the car on the chassis dynamometer. One major difference among these three standards is the speed-time graph or simply refer as driving cycle.
EU Standard used the NEDC (where urban cycle and extra cycle are two components for NEDC) [3] whereas the Japanese Standard used the JC08 cycle [4].
With simple mathematics, the gradient of the speed-time graph is the acceleration. We can see that NEDC has constant acceleration whereas JC08 has a rapid change in speed. In theory (as seen in previous topics), vehicle should consume more fuel with the driving behaviour that has rapid change in speed. However, recalled the formula for kinetic energy, the kinetic energy is directly proportional to the vehicle speed in the power of 2.
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| Just Refresh Memory on Previous Topics |
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| Rough prediction on minimum fuel requirement for the acceleration from 0km/h to 83km/h |
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| Rough prediction on minimum fuel requirement for the acceleration from 83km/h to 0km/h |
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| Red Region: Kinetic Energy from 0km/h to 85km/h Blue Region: Kinetic Energy from 85km/h to 120km/h |
Above calculations and the graph are used to demonstrate the significance of vehicle speed that affect the overall work done. Even though NEDC only has constant acceleration driving pattern however the overall work done from 83km/h to 120km/h is greater than the overall work done from 0 to 83km/h.
Therefore, it is difficult to judge which standard are harder for the vehicle to achieve better fuel consumption rating since
- EU Standard expected the vehicle fuel consumption performance up to 120km/h.
- Japanese Standard expected rapid change in speed frequently.
However, there are reasoning why each policy makers wanted their driving cycle in that ways. NEDC has longer history than JC08 therefore it is more standardized test that want to test the full potential of the vehicle however JC08 reflect the real driving condition in a city because there will no constant speed and acceleration in reality and it is unlikely to drive more than 90km/h in a city unless it is a highway.
Therefore, I will advise you to think this way,
If you prefer a realistic condition, Japanese Fuel Consumption Rating is more suitable for you.
If you prefer a standard that show the full capacity of the vehicle's performance, then EU Fuel Consumption Rating is more suitable for you.
Hopefully, my readers have clearer understanding the meaning behind JC08 rating and Urban/Extra Urban Cycle rating.
Meanwhile, different countries would adopt different Exhaust Emissions Standard eventually some car dealers outside of Europe, Japan and USA would just show the fuel consumption rating without specifying which standard.
If you want to learn more about the Vehicular Exhaust Emissions in different countries, there is a e-booklet[5] which is available online and free. Hopefully, your local country's environmental policies will be shown in this e-booklet.
Next time, you visit a car shop and you placed fuel economy as your highest priority in consideration, you may challenge the car dealer about which standard they refer about the rated fuel consumption value.
References:
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