Drivetrain Drag on a Prius

Thanks Patrick. I understand that it doesn't change the compression ratio.
I guess my wording was confusing. I meant that the higher octane would allow the fuel to reach a higher compression without pre-ignition, thus allowing the timing to be advanced resulting in a longer power stroke. The energy level in a premium grade is basically the same as in a regular grade. The increase in power is the result of the higher octane allowing the fuel to reach a higher compression resulting in higher efficiency and more power. The octane has no energy content. It is my understanding that most gas comes through the same pipelines. Additives including octane is added at the storage facilities, producing the different brands and grades. All gas coming though the pipeline has the same energy content. Octane is added to create the different grades. This is my understanding and while there are exceptions to the rule, this is how it generally works. If true, I was just thinking that the actual octane may vary from brand to brand and even within brands for a specific grade since it is added later. Spot testing has shown this to be true. And, if so, the results of difference brands having "higher enery" ratings, could possibly be the result of differences in octane, since the energy content of different brands theoretically are the same. Unless, of course they have a seperate delivery system. Thank you for you patients. Just trying to understand. :noidea:

 

No problem. Sometimes I'm a little too brief not realizing it might seem abrupt. I like detail but sometimes folks are not quite ready for it.

Here are the graphs:

These tests were conducted in April, 2007, the winter blend. You'll notice a slight improvement in high octane fuel at the highest power settings but these are not high mileage power levels.


These tests were run in July 2007, the summer blend.

My fuel testing protocol is:

• replace fuel in tank - run the car to ICE stop and put 1 gallon of next sample in tank and then drive to gas station to put in 4 gallons of the next sample.
• wait for standard day - ~70F (21C), no wind, dry.
• configure Graham scanner - recording data to a laptop via the serial interface. The polling interval is about 1 sec. for six data values.
• warm car - drive for at 20-30 minutes to throughly warm the car
• standard hill climb - my hill is 525 ft., ~160 m. approached on cruise control at 55 mph.
• excel analysis - load data points and use trend line function to smooth data points.

I also wanted to find out if the density might give a non-destruct way to assay energy density:

However, I could not find a correlation between gasoline density and the subsequent energy density. I was surprised that Exxon was an outlier and BP was in the pack. These were summer blends and testing winter blends may give a different result. I'll have to wait to January/February to tell.

Bob Wilson

 

Thanks this will take awhile to digest. You've certainly put alot of work into it. I appreciate in information.

 

It's a simple matter of kinetic energy. If both vehicles start at the same velocity, the heavier vehicle will glide further.
Kinetic Energy (KE) = KE = 0.5 x mass x velocity^2

It will take more friction/drag to make the heavier Prius stop at the same distance as the Smart.

Another example. Take a 15lbs bowling ball and a 8lbs one. launch them at the same velocity. The heavier ball will "glide" further due to its higher initial Kinetic Energy.

Knowing the weight of both cars, calculate the speed at which they would have the same Kinetic Energy (The Smart would have to be a bit faster). You can then make your glide test and you will find out which car has the higher parasitic mechanical drag.

I did a quick calculation. Using your stated vehicle weight of 820kg (Smart) and 1330kg (Prius), adding a 100kg passenger (920kg, 1430kg), your test needs the smart to start its glide at 76km/h (20.8m/s) and the Prius at 60 km/h (16.7m/s). Both cars would have a initial kinetic energy of 198-199k Joules. Make sure both have the same amount of fuel in the tank.

At these velocities the aerodynamic drag may affect the results. The same test could be done at 37.5 km/h for the Smart and 30 km/h for the Prius (49k Joules). Do the test and let the cars glide to a stop, see which one goes further. At low velocity the aerodynamic drag will be a lesser contributor and this will put the emphasis on the parasitic mechanical friction loss.

 

It would still be a very interesting test.

And BTW you are very cool to have both a Prius and a Smart.

 

Maybe they'll let you use the track at Derby Downs in Akron, Ohio.