Acceleration and mpg

I'm averaging 53-56 mpg (6000 mi on odometer). I accelerate up to about 28 mph, then engage the cruise control. I use the cruise control to accelerate up to the desired speed (average 66 mph). This produces optimum fuel economy and battery recharge.

I commute 30 mi each way Mon-Fri (60 mi total each day) on a highway. I end up each trip with a green battery and good fuel economy. I have run the heater quite a bit this winter, but not the window defrosters. Morning drives are usually with headlights on. I use Mobil 1 oil.

I make every effort to anticipate stop lights, signs and traffic on surface streets. I refuel at the last blinking bar (to minimize mass of the gas in the tank). The vehicle is parked in a well-insulated, but unheated garage.

 

the Prius engine is very efficient in design and the amout of fuel use in to accelerate to say 100K-60mph is best used in the engines most efficient rpm range, about 3000 rpm. This rpm will accelerate the car quite briskly to speed. So to break it down, best rpm=shortest time to speed (within reason) bonus is best mpg.

 

The instantaneous MPG will be lower, but for a shorter time.

To get up to a certain speed, you just need to supply (1/2)*mass*(velocity squared) energy, independent of acceleration. The only way the rate of acceleration comes into play is with the engine efficiency curve. Putting the pedal to the metal makes the engines work outside their peak efficiency, but moderately brisk acceleration should keep you within the range of good efficiency. Ridiculously low acceleration can be bad in that the ratio of work done by the engine to move the car, relative to overcoming friction in the engine, can be worse.

As others have pointed out, it would make a lot more sense if the display of miles per gallon was plotted as a function of distance rather than time...

 

I find that getting up to speed in the shortest amount of time (reasonable, not rocket-like), gets me better MPG for the simple reason that I'm spending WAY more time at speed (good MPG), than getting up to speed (low MPG). More time spent in that 50 MPG part of the bar graph means the overall average will be around 50. I find if I stay at a slow acceleration, I'm way under 50 MPG for a longer period of time, thus, the overall average is lower. I love the fact that I can beat everyone off the line and still manage around 50 MPG! What a concept: drive fast (or quickly) to get better MPG. Try that in non-HSD cars, the results are not as good. Love my Prius.

 

skruse is your mpg from hand calculations or the car computer? I am getting around 57.5 mpg but that is what the computer says. I am thinking I am around 52 mpg in reality.

I find that the faster I get to my desired speed and then cruise at that speed the better MPG I get. it is easier on the engine to maintain a speed than to constantly accelerate. However, it is a brisk accelaration (maybe about 1 mpg per sec or there abouts). Too fast and you burn up too much fuel too slow and you are also burning up fuel. You need the happy medium.

 

This acceleration issue is complicated and there seems to be very little agreement.

First I have seen very different descriptions of "brisk". Then I have seen advocates of
accelerating with no arrows, which in my car is anything but brisk, though it seems to
vary so much with temerature I gave up trying it.

But here are some things to consider:

1 The guy in Japan that got 1000 miles on a tank appears to have done so by brisk
accelearation combined with engine off coasting if I understand him correctly. I can
see how this would be the ultmate.

2 But in the real world even though you could argue that brisk acceleration is most
efficient for the engine, you are normally going to cruise with engine on afterward.
Someone would have to plot this out for me to prove it is significantly better. In this
case you are choosing best efficiency for a short time and then low efficiency for the
rest of the time vs just some medium efficiency for the whole time. If this give you more
than 1 mpg difference in regular driving I'd be surprised. Brisk does make some
sense to me for cases when you will then be able to coast after you get to speed. But I accelerate slower than most and still get great mileage, except in cold weather where nothing I do seems to matter other than extending my trip length.

3 The engine efficiency curves (recently posted again at yahoo) do show great efficiency at 4000 rpm. I think it was. So this should be an optimum point to run at considered by itself.

4 The idea of accelerating without battery discharge also makes sense since here you
have a path with added losses added, but again this is not the whole story, since you
have to consider that the battery charging load helps the engine run at more efficiency
while cruising along too by adding to the load.

5 One advantage of the Prius is the Atkinson engine which has advantages in high
efficiency over a broader hp range. And this is coupled with a drive system that
makes engine rpm essentially decoupled from road speed. So these make the
car different from a regular car even without considering the hybrid stuff.

6 As others have pointed out, we all have very different driving conditions and speed
limits, terrain, etc. So best thing is to use the Prius display and see what works best
for you. Not always possible unless you can test one thing at a time over 5 minutes
but still worth trying if you can get away from the traffic.

7 In cold weather what works is often different from what works in warm. Here a
major priority is to keep the engine warm. This affects the routes I take to work etc.
Also you get some idea what the engine can do since the battery is often almost shut
down once you get going. You get arrows but the currents are kept very low.

 

1000 miles on a tank? Whoa he is da man. I can keep my MPG at 99.9 as long as I do not exceed 25 mph and accelerate very slow to avoid kicking in the ICE except to charge the battery. I wonder if his altitude also makes a difference?

 

The fuel tank is bigger in Japan. The real story is the guy in the US who got 967 miles on one tank. He averaged 35 mph for almost 30 hours with no AC and the window rolled up on all back roads between Pennsylvania and Florida. I saw a picture of his display. He ran out of gas going up a hill or else he might have made 1000.

 

I like the "riding a bicycle" analogy regarding rapid acceleration. As one who rides a bicycle I start rapidly but not overkill (that ensures fatigue for the rest of the ride). I drive gently, always trying to optimize efficiency.

As far as fuel economy, I keep my own records and do not rely on the MFD read out.

 

the real story of a real crazy guy... i never would have sweated all over the inside of my Prius for that.

hmmm... thats 0-60 in a minute. 3 miles per second is moderate acceleration.

one thing i found concerning acceleration and good gas mileage. the more of one you do, the less of the other you will achieve.

 

oh yeah maybe it was 1 mph every 3 sec. Hard to tell was paying attention to traffic. Basically not gunning it but not slow poking it also. When I drive home tonight I will have to see how fast I accelerate.

 

About that, I heard about it, and might its ture. Because some Prius group member(in Japan) is try to squeeze out extra mpg. Also, I been seen the online post before which reagrading how to gain extra mpg.

 

While we are at it, can someone simply explain why we express fuel economy in "miles per gallon," and countries using SI units express fuel economy as "Liters per 100 kilometers"?

Use of measuring units in this way is reversed (in comparision to each method). Is there a conversion factor (dimensional analysis) to go from "miles per gallon" to "kilometers per Liter" or "Liters per 100 kilometers"?

 

so your second tank was 4.238 L.per 100 Km. and your 10th tank was 4.200L per 100Km. try this url for a good conversion utility. http://www.packexpo.com/education/ref/fuel..._conv_cal.shtml

 

Here in Japan, the read out on my Classic prius is km/litre - the best conversion site I have found is here:

http://www.convert-me.com/en/convert/fuel

I am pleased to be averaging 21.3 kms/litre or 50.1 MPG (US) during the coldest weather (+- 6C) we have had this year.

Jef

 

Maybe, this is another annual record going all downhill.
(Posted sometime ago, but the post was gone by the server crash.)

I would like to report that a Japanese Mileage Master called EPV2(his handle) achieved more than 1,500km(970miles)/tank through out a year.
His one year data is...
distance 26,547.6km(16,499.4M)
GAS used 843.71L(222.91G)
Mileage 31.47km/L(74.02MPG)

His driving style is...
- Never drive on Highway where ICE always needs to run.
(He took another car if he drove on highway. 60MPG on highway is possible but his target was more than 70MPG avg.)
- Use ICE only on accelerating and going uphill.
- Never drive with heavy motor only mode where we'll see rebound on later worse mileage for battery charging.

A term "briskly" is vary vague I think.
Watch your energy screen on MFD,,,,Oh, no, correction, watch your road, traffic, pedestrian and etc,
then glance at energy screen.

Best briskly acceleration - No arrow to and from HV battery.
Good briskly acceleration - Green arrow to HV battery.
Bad briskly acceleration - Yellow arrow from HV battery.

Regards,
Ken@Japan

 

Regardless of how one might feel, the physics is simple: the total energy required to get up to a particular speed is independent of the rate of acceleration. To first order, the rate of acceleration matters not at all. To second order, you're best off at the peak of the engine efficiency curve.