A fuel consumption and efficiency study in way too much detail


(via MAKEzine blog)

Matthew Vea owns a 2006 Jeep Wrangler Unlimited.  With the horrendous cost of gas we all suffer under now, he decided to learn a bit more about his Jeep’s fuel consumption, where the sweet spot for driving is, how much gearing, cruise-control or manual speed control, air condition usage, and more affected fuel consumption, and all the other dirty details someone who would even take on this project can find out.

Starting with hooking up an OBD-II tool (a computer for performance monitoring) to his Jeep’s computer, he tracked pretty much everything he could to see how it all ties together.  The end result is a huge, detailed write-up to all the data he gathered.  For me, on a 1024×768 screen, the final document is about 40 screens worth of text and images.  When I say it’s way too much detail, I mean that for the average reader, it’s more than one will likely read through.  But if you take time to read even a few sections of the article, you can learn a lot about how to test your vehicle, as well as getting a few ideas that will probably help you improve your fuel efficiency.

Also, the end of the article has almost 100 links to articles the Matthew links as back-up to what he writes.  This is a rich resource for anyone interested in studying or improving fuel consumption and vehicle performance.

I own a 2006 Jeep Wrangler Unlimited. This vehicle is actually an upgrade from my previous 2004 Jeep Wrangler Sport. My first Jeep did not have any air conditioning or a cruise control. After spending a year in the desert heat of Iraq, I vowed to myself that if it were in my control, then never again would I go without air conditioning. So, I figured if I was going to burn gas up in my 4×4, I may as well burn it up a little more comfortably.

. . .

For saving gas, there are three courses of action. First, driving style affects fuel efficiency. Many people cite “rules of thumb,” but most cannot back these claims up with evidence. To learn the truth about driving style, I conducted road tests with a computer interface hooked into my engine. The second way to improve fuel efficiency is to modify the way an engine performs. Modifications take many forms so I browsed the Internet to find the most common and analyzed the fact and fiction behind their performance. Lastly, the very fuel that goes into an engine plays a role in efficiency. With all the talk of alternative fuels these days, I wanted to know what they are, whether they work in my engine and how they compare to regular gasoline. Ultimately, I take all the cards relating to fuel efficiency and lay them on the table for scrutiny.

I used the following equipment to collect performance data:

  • OBDII interface tool – The specific interface tool I used was the ElmScan5 – a multi-protocol reader offering improved performance over the previous versions. It is a hardware device based on the Elm327 chip (an upgrade over the Elm323) which converts the esoteric electric signal interface from the car into a human understandable, ASCII format. It is capable of reading approximately four data samples per second and connects via the computer’s serial port.
  • Software from DigiMoto – The software from DigiMoto interfaces with devices built upon the Elm32x chipset and supports selectively reading engine parameters, data logging and a ‘poor mans’ dynometer.
  • Microsoft Excel – Once collected, I imported my data into Excel for later analysis.
  • Laptop Computer
  • My Trusty Jeep Wrangler Unlimited

He goes from here to write up how the OBD-II works, and then starts the details of what he measured and how he tested.

Before differing driving habits can be analyzed, it is important to understand exactly what the engine is doing. Quantitative data may then be compared against this background. Once the engine basics are outlined, I will collect data and analyze the results for:

  • impact of driving at various speeds
  • effects of unnecessary loads on the engine
  • comparing cruise control to manual control
  • benefits of drafting
  • difference between fast and slow acceleration

After this comes the flood of data, along with explanations of how all this information ties together to give meaningful results.  Power consumption, friction, airflow impact, high RPM and low RPM results, air friction and drafting, and on and on.  If you have any interest at all in how to do this on your own or where to learn how to improve your vehicle’s performance, Matthew’s article is sure to be an excellent start.

[tags]Vehicle performance, Fuel efficiency, Performance testing[/tags]

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