Sitting at stop lights and MPG

<div class='quotetop'>QUOTE(9G-man @ Oct 9 2007, 01:40 PM) [snapback]523219[/snapback]</div>

I apologize, and admit my mistake. I read your post multiple times before I responded, and yet every time I read it, somehow, my mind apparently replaced the word gallon with the word tank. I was sure that you said that both cars start with one tank of gas.

Yes, if both cars start with identical amounts of fuel, and they both drive the same distance and then are left to “idle†until they are out of fuel, then they will both get identical mpg as long as a distance is chosen that both cars are capable of traveling with the chosen amount of fuel. As others have mentioned the significant difference will be in the amount of time it takes each car to run out of fuel.

Of course your example has a fuel quantity chosen for each car specifically to get the result you wanted. It is possible to get anywhere from 0 mpg to infinite mpg in the Prius if the parameters are chosen to yield the results desired.

 

<div class='quotetop'>QUOTE(9G-man @ Oct 9 2007, 02:43 PM) [snapback]523247[/snapback]</div>

Assuming that we are referring to the cumulative and instantaneous numbers displayed and not the bar charts, then yes 0 MPG is 0 miles traveled. It tells you nothing about how much fuel you’ve burned, and only about how much distance you’ve traveled. Depending on how much fuel is burned when it happens, it can play huge roll in overall mpg as you demonstrated in your earlier example.

On the other hand, while 99.9 MPG electric is infinite MPG, 99.9 MPG is not necessarily infinite mpg. 99.9 MPG is anything greater than or equal to 99.85 MPG, up to and including infinite mpg. How much it contributes to overall MPG depends on what the actual MPG is.

Example:
Car drives 1 mile at 50 MPG, and a second mile at 100 MPG with the display reading 99. 9 MPG. Overall MPG = 75 MPG

Car drives 1 mile at 50 MPG and a second mile coasting down a hill with the ICE off and the display reading 99.9 MPG. Overall MPG = 100 MPG

I’m not sure what you mean by “ultimate advantageâ€, but it seems to me that there are 2 things about the Prius that contribute significantly to it’s ability to achieve relatively high fuel efficiency, the Atkinson Cycle engine, and the ability to turn the ICE off when it isn’t needed (coasting, decelerating, and stopped). The first significantly reduces the amount of fuel used when the ICE is needed, and the second significantly reduces the amount of fuel used when the ICE is not needed.

My driving is over 90% highway at speeds of 55 MPH or higher. The ICE rarely shuts off so the “infinite MPG†plays little roll in my overall MPG. I average a little under 56 MPG almost entirely because of the highly fuel efficient Atkinson Cycle Engine. For my daily route and my driving style, the “infinite MPG†is not the “ultimate advantageâ€.

 

<div class='quotetop'>QUOTE(cheminee @ Oct 9 2007, 01:49 AM) [snapback]523002[/snapback]</div>

Well, there is an issue with the bar graphs which are a bit confusing. If you are not moving the bar graph reads 0 whether the engine is running or not. In other words, when the engine is running and the MPG for that instant is truly 0 (0 miles divided by the amount of gas consumed by the idling engine). On the other hand, if the engine stops, the bar graph reads exactly the same, but the math is much different (0 miles divide by 0 gallons). Understandable why the bar graph does this since 0/0 is undefined except in some particular types of math problems that we don't need to get into).

However, the important point is that the bar graph showing 0 does not necessarily affect the numeric MPG reading shown at the bottom of the screen.

I'm not sure if that helped more made things worse

 

<div class='quotetop'>QUOTE(cheminee @ Oct 8 2007, 12:59 PM) [snapback]522799[/snapback]</div>

With the Prius you get similar mileage when its stop and go traffic and excessive idle periods , as you would with nonstop city driving .
Whereas any other ICE vehicle will get way below their expected MPG with stop and go traffic and excessive idle periods.
Ive had the same thought.The computer doesnt factor in idle time at lights or traffic jams.
The Prius idle off can be a huge savings compared to a regular vehicle and that isnt actually measured .

 

I think that if you do 100% highway driving where you only start from stationary at the start of the journey and only stop at the end, you travel almost your entire journey above 50 mph on flat roads there are more than 2 aspects of the Prius that allow you to achieve excellent mileage.

Atkinson Cycle Engine: a very efficient engine but with low torque
ICE shut down when coasting: No petrol used when coasting down hill or stopping
Electric boost: Allows the Atkinson Cycle engine of modest displacement to be used with reasonable acceleration
Infinitely variable transmission: The engine is kept at its most efficient load and RPM
Extraordinary low air drag: The prius has the lowest drag of any 4-door sedan in production at 0.26Cd
Low rolling resistant tyres: 30% of the power is used to overcome rolling resistance so small reductions here yield big gains
Regenerative braking: Captures what would be waste energy storing it to later propel the vehicle
MFD: Interacts with the driver to influence driving style sometimes imperceptibly

I’m sure there are more.

 

Not quite right. 1 mile at 50 MPG uses .02 gallons. 1 mile at 100 MPG uses .01 gallons. 2 miles using .03 gallons equals 66.7 MPG.

Second example is correct.

Both our truck and van have MPG guages. When waitng at a traffic signal, you can see the average MPG drop, especially right after a fill-up.