Motor Trend Magazine teamed up with Emission Analytics and Chevron in order to accurately measure mileage under real world driving conditions. The project is called the Real MPG Program.
It’s not as easy as you think to get accurate and repeatable mileage data. You can’t just drive around town, make a few passes down the highway, and then fill’er up and see how much gas you used. There are so many variables that come into play such as; fuel, atmospheric conditions, wind speed and direction, tire pressure, air conditioning on/off, windows up/down, driving style etc… You get the picture. Motor Trend had been looking for a way to accurately monitor fuel usage without modifying the vehicle. After all, these cars are loaners given to the magazine for review purposes. The manufactures wouldn’t take kindly to any modifications to the fuel system, like the addition of a fuel flow meter.
Emission Analytics came up with an accurate resolution to the problem without altering the fuel system in any way. Basically they channel the exhaust through a device that measures the flow rate and the concentrations of CO and CO2. In their own words here’s how they do it: “We calculate the fuel’s burn rate by capturing the exhaust pipe’s gaseous emittance; measure its flow rate, analyze a sample of it to determine its concentrations of CO and CO2; and then walk back the math to figure out-every single second, mind you-how much gasoline is being burned to produce these numbers.”
Next, a chemically consistent fuel supply is needed because Gasoline’s energy density can vary by about 4% between stations. Chevron, who by the way participates in the “Top Tier Gasoline” program, supplied 15,000 gallons of regular, premium, and diesel fuels for this project. They also periodically sample the fuel to monitor its condition to insure consistency.
Another critical component is Emission Analytics test track, which consists of 88 miles of real road driving conditions. The course is made up of 55/45 % city/highway driving. The route is driven in both directions, and some sections are repeated to check for consistency. They test with and without air conditioning and they welcome typical traffic. However, any traffic outside of the norm flags the run for a redo. GPS logging is used to keep track of the car’s speed. Over 10,000 miles have been driven testing the first 100 cars looking for their real world mileage. Here are some of the results I found most interesting:
- Combined City and Highway Mileage – 18% of the cars did better, and 17% did worse than the EPA estimates
- Fuel Consumption by Auto Manufacturer – Out of 23 manufacturers 11 did worse, 2 were the same, and 10 did better than their EPA estimates
- Highway VS City Driving – On average Highway driving improves mileage 26% over City driving
- Air Conditioning Penalty – Air conditioning will cost you a 1% decrease in mileage for Highway driving, and a 5% decrease for City driving
- Aggressive Driving – Smaller displacement engines suffer a larger percentage decrease in mileage than larger displacement engines do
- Aggressive Driving and Traffic Congestion – decreases mileage by 11%
I recommend that you look at the Real MPG article at Motor Trend. There you will find a detailed explanation of the program. Motor Trend continues to add to the list of cars tested. They are now on a mission to collect and analyze the data from the second 100 cars. To quote them, “See you at 200!” Click here for the report card on the first 100 cars.
Next you have to check out the Real MPG home page at Motor Trend. There you select your Vehicle, Road Type, Traffic Level, Driving Style, and Air Conditioning usage. After your selections are made your Real MPG is calculated and displayed along with the EPA estimates for comparison. It’s pretty slick. Give it a try and see how different driving conditions affect your mileage estimates.
I hope you found this Real MPG Program article interesting and useful. Look for more articles on MPG to follow.
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