Getting a 1,000 mile tank
#1
05-19-2007, 12:59 PM
Join Date: Oct 2005
Location: Huntsville, AL
Posts: 5,613
Getting a 1,000 mile tank
Hi folks,
Some of us are looking at the Prius low-speed performance. Ken's recent success at getting a 1,000 mile tank and over 50 Japanese enthusiasts who have done the same has gotten me looking at the problem:
> . . . So
> this leads to a strategy for a maximum mileage effort:
>
> 1) steady state at 18 mph
> 2) pulse and glide 15-22 mph
Last night, I did a quick, informal test at a steady speed of ~18 mph and a Pulse and Glide that came in at an average speed of 19 mph. The protocol, two passes, opposite directions, of the same 'flat' test track after sundown with no significant wind. I have not calculated the drag but the energy results were somewhat surprising:
STEADY SPEED:
Unexpected, the first steady speed pass had the engine running the whole time but at a very low power setting. The specific ICE output was about 10,000 J/g. In contrast, the shorter duration, ICE interval on the second pass was about 15,000 J/g, a previously observed value. In both cases the peak J/g occurred at ~1,200 rpm and the lower relative values were at higher rpms that scattered up to ~1,500 rpm.
15-25 PULSE AND GLIDE:
The pulse and glide gave a slightly higher average speed, 19 mph, but the energy in Joules/meter, was significantly higher, 299 J/m versus 255 J/m. This is something I had expected because of the energy lost starting and stopping the ICE.
This rough data suggests an optimum mileage strategy would be a constant speed in the ~18 mph, +/- 3 mph, but operating the car so the ICE runs to charge the battery and then cycles off to let the stored battery energy sustain the speed. In contrast, Pulse and Glide stores the vehicle energy as kinetic energy, not battery energy. The Prius power cycling is less a 'pulse and glide' as much as switching between two Prius unique modes:
1) ICE on and battery charging
2) ICE off and battery sustaining
Using 15,000 J/g, ICE specific energy from tests with Shell 87, with 255 J/m at 18 mph and Wiki sources on gasoline density, it looks like we should achieve 104 MPG. It would take a little less than 10 gallons to achieve 1,000 miles in about 55 hours for an NHW11. An NHW20 should achieve better than my NHW11 data.
One side comment, it is not fun trying to drive at 18 mph. I need to finish my home-grown cruise control before trying this. Trying to do it as part of the normal work week will be a challenge but much easier if I can get my smart cruise control together.
Bob Wilson
Some of us are looking at the Prius low-speed performance. Ken's recent success at getting a 1,000 mile tank and over 50 Japanese enthusiasts who have done the same has gotten me looking at the problem:
> . . . So
> this leads to a strategy for a maximum mileage effort:
>
> 1) steady state at 18 mph
> 2) pulse and glide 15-22 mph
Last night, I did a quick, informal test at a steady speed of ~18 mph and a Pulse and Glide that came in at an average speed of 19 mph. The protocol, two passes, opposite directions, of the same 'flat' test track after sundown with no significant wind. I have not calculated the drag but the energy results were somewhat surprising:
STEADY SPEED:
Unexpected, the first steady speed pass had the engine running the whole time but at a very low power setting. The specific ICE output was about 10,000 J/g. In contrast, the shorter duration, ICE interval on the second pass was about 15,000 J/g, a previously observed value. In both cases the peak J/g occurred at ~1,200 rpm and the lower relative values were at higher rpms that scattered up to ~1,500 rpm.
15-25 PULSE AND GLIDE:
The pulse and glide gave a slightly higher average speed, 19 mph, but the energy in Joules/meter, was significantly higher, 299 J/m versus 255 J/m. This is something I had expected because of the energy lost starting and stopping the ICE.
This rough data suggests an optimum mileage strategy would be a constant speed in the ~18 mph, +/- 3 mph, but operating the car so the ICE runs to charge the battery and then cycles off to let the stored battery energy sustain the speed. In contrast, Pulse and Glide stores the vehicle energy as kinetic energy, not battery energy. The Prius power cycling is less a 'pulse and glide' as much as switching between two Prius unique modes:
1) ICE on and battery charging
2) ICE off and battery sustaining
Using 15,000 J/g, ICE specific energy from tests with Shell 87, with 255 J/m at 18 mph and Wiki sources on gasoline density, it looks like we should achieve 104 MPG. It would take a little less than 10 gallons to achieve 1,000 miles in about 55 hours for an NHW11. An NHW20 should achieve better than my NHW11 data.
One side comment, it is not fun trying to drive at 18 mph. I need to finish my home-grown cruise control before trying this. Trying to do it as part of the normal work week will be a challenge but much easier if I can get my smart cruise control together.
Bob Wilson
Last edited by bwilson4web; 05-19-2007 at 01:02 PM.
#2
05-21-2007, 07:44 AM
Re: Getting a 1,000 mile tank
A non-technical approach might be to fuel up at Leadville, Colorado, above 10,000 feet. I think these are the 'highest' gasoline stations in the US. Then, find the all-downhill path to the Texas coast, more than 1000 miles away. You might make it...
I bet that Bob could tell us the 'effective energy content" of fuel purchased at any altitude.
DAS
I bet that Bob could tell us the 'effective energy content" of fuel purchased at any altitude.
DAS
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