Graphics of average fuel economy vs speed

Thanks! You're headed in an interesting area that I've started moving towards. I'm using the Auto Enginuity package. But last year, I used fixed benchmarks to generate these graphs:


Also,


I've got some data at home I'm planning to reduce so we'll have something to compare.

Since you are new to this forum, you might want to try putting some of the data in a table:

• Use the "[" and "]" to identify the keywords
• Use "table" to begin a table
• For the first row with headers, use "|" to separate the titles
• For all subsequent rows, separate data with "|"
• Last row ends with "/table" between the "[" and "]"

One thing, how do you normalize the temperature and road grade for the different samples? I get the impression these are collections of many small samples over time intervals measured in months or even a year, right?

The reason I ask is we know temperature and road conditions can have a substantial impact on vehicle mileage. Also, small samples can easily suffer from unexpected bias. Understand, I applaud your initiative but want to understand more about your data and how temperature and road conditions are 'held constant.'

Thanks,
Bob Wilson

 

Correct as this comes from my days as a private pilot. We needed such charts to calculate the fuel consumption as a function of speed to determine our range. When flying, it is important to reach the destination airport with enough fuel reserve to land.

In cross country driving, this type of chart allows us to make decisions on how much fuel will be burned. As a general rule, such driving does not include a lot of inertial losses, the acceleration and decelleration.

I have to think about this for a bit. My charts are aimed at trip planning where warm-up and inertial fuel costs to reach cruise speed are a very small fraction of the fuel burn. I don't see how your chart provides the information to make similar planning decisions BUT these charts are new to me. I don't have a good model of their use.

I noticed that and wanted to share some work I'd done with the NHW11 Prius:

This chart uses the vehicle drag formula to calculate the energy needed to sustain any given speed. Then we add the vehicle overhead, a fixed amount needed to run the computers, lights and other electrical loads. At lower speeds, the fixed overhead predominates eventually reaching the least efficient speed, the car turned on and not moving.

I suspect if you gathered data from several hours at a very low speed, 5 mph (8 km/h), you would capture not only the highly efficient electric modes but also the fuel consumed to run and charge the traction batteries. Ordinarily we spend very little of our time at such slow speeds, which means the energy needed by the vehicle at the slow speeds from multiple samples, is hidden in the higher speed samples.

Thanks, I'll take a look later. I've made an assumption you are using just the fuel burn to calculate the mileage and do not have the traction battery energy flow, the total energy flow.

This is an interesting approach and once I have a chance to deal with some of my Auto Enginuity data, it may help us understand the utility of this approach. I'm not skeptical as much trying to wrap my head around the data approach and its utility.

LATE THOUGHT:

Thank you for providing SAE units in the second chart. I'm humbled to have not provided metric for my data . . . well time to do the right thing. What I noticed is your chart above ~60 mph begins to match my data, which makes sense. At higher speeds, our Prius is working in 'gas engine' mode without significant energy flows to and from the traction battery.

Bob Wilson

 

Hi Frank,

I made a metric version of this chart but even using SAE units, it illustrates the challenge of calculating MPG vs MPH graphs:

The "blue" line is the engine coolant temperature and the "red" line is the speed on this trip. All data was recorded with an Auto Enginuity then I used the MPH and Mass Air Flow (gm/s) to calculate the mileage in these ways:

• solid green line - is the average of the total miles to that point divided by the total fuel consumed at that point. This chart shows the warm-up penalty we pay everytime we first start the car. With the engine coolant, we can see that engine efficiency is a strong function of coolant temperature.
• small green diamonds - are the miles per gallon calculated between every two sets of observations. It is the instantaneous MPG.
• orange line - is what happens to a trip meter that is reset after achieving a constant speed on a flat or known route. It works by accumulating the distance divided by the MPG and always ends with the average MPG from when it was reset.
• purple line benchmark - is the difference in distance between two time intervals divided by the difference in fuel consumed between the two time intervals.

One thing this chart shows is the distortions from:

1. warm-up overhead - the engine coolant really needs to reach a steady state before the engine efficiency steadies out. During warm-up, there is too much variability in fuel consumption to come up with reproducible results.
2. inertial overhead - acceleration and even decelleration badly distort the mileage. So too can ascending or descending hills (not shown.) Although we can use Newton's Laws to explain and model them, as individual observations, it is hard to make any use of them.

If you have the engine coolant, velocity, and altitude data, you might trim out data point outside of warm-up, steady-state, level ranges and then your mph vs MPH should come closer to what I would expect to see. . . . just a thought. This is by the way I intend to use Auto Enginuity data to plot more detailed mph vs MPH charts. However, I really want the traction battery current and voltage to handle vehicle overhead and deal with hybrid modes, speeds under 42-46 mph.

Here is the metric version:


I took the same data and using just the instantaneous fuel consumption rate, sorted the data and calculated an average fuel consumption rate to generate this chart:

NOTE: single entry and zero entries were trimmed out. Also, I rounded the km/h to the nearest value although it wasn't technically required.

Bob Wilson

 

This is good, how collaboration works. There aren't very many who take the time to record the data. However, I need mph vs MPG data to estimate fuel burn for cross country trips.

One thing I don't understand are the vehicle motions prior to ~06:15. I assume those are minutes:seconds? My North American ZVW30 starts the engine within ~15-20 seconds. It is not unusual to find European and Japanese Prius have different control laws. Is a delayed engine start measuring minutes common or was EV or something else used to suppress starting the engine?

I used a simpler technique. I sorted the MAF data and found the lower limit of valid MAF values. I then used a formula to exclude these samples.

Bob Wilson

 

Interesting use of EV button. I tend to approach the house on flat land, at low speed, to use the traction battery to reach home at a low state of charge. My traction battery seldom has enough charge to run in EV mode upon first start in the morning.

You may have the data to answer some questions I have:

• What is ending trip MPG versus time duration of trip? Two lines, one at starting ~20C versus a higher temperature (aka., warmed up.)
• Similar to above, what is ending trip MPG versus distance of trip?

We both see a significant impact when the engine first comes on. However, as the vehicle warms up, the mileage improves. It would be great to know the range of "short trips' that are in the high fuel consumption range. For example, trips shorter than ~5-6 miles (8-10 km) appear to be very poor mileage trips. But if the trip is longer, the fuel efficiency significantly improves.

Bob Wilson

 

Good work again Frank, would it be possible to get the metric version as well ?

:hail: Many thanks for your work and your time.

 

I notice a few interesting anomalies in this data; for example, 54 mph/87 kph (and to a lesser extent, 88 kph) is a bit of an outlier, with ~25% more readings than the surrounding data points. This tells me that you probably drive with cruise control set to 54-55 (or you might stay at that speed manually). Looking at the wiggles in the fuel economy curve there, you'll notice that the FE goes up as you pass 54 mph, and dips down just below that speed. This is an artifact of having a set speed - when you're at 53 mph, you're typically accelerating, and you get worse fuel economy. When you're at 55, you're usually coasting, and you get better fuel economy.

I'd bet there are other wiggles in this graph that are similarly explained - such as the dip in both sample count and FE around 36 mph/58 kph; I'm guessing you don't go that speed often, except when you're either speeding up or slowing down, and the repeated acceleration through that point probably causes that 8 mpg wiggle in the curve.

Just something to keep in mind as you look at the data here...

 

Gotcha, I didn't realize the thread was that old, and completely missed the beginning of it when I hit the "view first unread" link.

 

Hello Frank:
I've read your post regarding fuel consumption.
I would like to ask you if you have the following info:
In a distance of 100 Km what will be the consumption of a 2.4L; 4 cyl.; gasoline engine in the followin speeds:

From 0 to 50 Km/h
from 50 to 90 Km/h
from 90 to 120 Km/h
and ...at more than 120 Km/h.

Will wait for your comments.

Best regards...

Jose Luis

 

Do you realize you are replying to a post from over 6 years ago?
This is a very old thread.