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I am designing a GPS based acceleration meter for car. I'm planning to give user some scores based on his various acceleration practices. Not going to the electronics part of GPS, i want to know in what acceleration/braking range, fuel economy of any average 1000-1500cc car is maximum? Any chart including acceleration/deacceleration range vs fuel economy effect.

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    This is an impossible question to answer, unless you have a seriously clever GPS system - is the car going uphill or down? Which gear are they in? What are the prevailing traffic conditions or road conditions? Are they accelerating up a particularly short slip road, or pulling away from a junction in heavy traffic - both of which would need more acceleration than normal? – Nick C Jun 23 '14 at 9:40
  • @NickC some websites/links do suggests that an acceleration of ~1.5m/s^2 is considered to be an ideal and economical one. But i wanted to confirm it and not going by just what that website claims – user3098378 Jun 23 '14 at 10:36
  • Usually it is said an engine produces the best work/energy ratio at peak torque. This is one of the principles behind the CVT. This may help you in figuring out what you want to know, because I'm really not sure what you are even asking. – Pᴀᴜʟsᴛᴇʀ2 Jun 23 '14 at 11:03
  • @Paulster2 you might know that when we excessively accelerate our car, more fuel is consumed. Same is the case with hard braking. What i asked is, a general value of acceleration( metre/sq. sec) which is an ideal one and is economical in terms of fuel economy and consumption – user3098378 Jun 23 '14 at 11:34
  • So, I think what I said about torque directly applies. Because of this, every car is going to be different. Agreeing with @NickC ... I don't think there is a "magic" equation which is going to give you this without some really extraordinary means. – Pᴀᴜʟsᴛᴇʀ2 Jun 23 '14 at 11:50
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There are no charts that I am aware of, but you can calculate the theoretical maximum efficiency by considering the following":

  1. the RPM
  2. current speed
  3. assume a volumetric efficiency of 100%
  4. Assume an ideal air/fuel mixture of 14.7/1 (for petrol engines)
  5. the weight of the car
  6. assume the car is traveling on a 100% level surface
  7. total volume of cylinders

considering these things, you should be able to calculate the theoretical maximum efficiency of a car.

Tip: you don't need the GPS to tell you your accelleration if you plan on reading info from the OBD port because you can use the difference in speed between two requests for current speed combined with the delta of time to calculate acceleration.

  • Your #3 is a bad assumption. Any vehicle used on the road which is not turbo/supercharged will not have a VE of 100%, more like 80-85%. Naturally aspirated race cars can reach somewhere around 102-104%, but that is through extraordinary means. – Pᴀᴜʟsᴛᴇʀ2 Jun 23 '14 at 11:55
  • A fair point, but we're after the theoretical maximum given ideal conditions. Like when we were using ideal gases in physics calculations that could be compressed to 0 volume. What I'm saying is that I am after the absolute mathematical limit of efficiency. – Captain Kenpachi Jun 23 '14 at 12:01
  • Actually, I missed the line about to calculate the theoretical maximum efficiency. Good point. – Pᴀᴜʟsᴛᴇʀ2 Jun 23 '14 at 12:14
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I think you can't use a single average value for all cars. Here are some variables that could greatly influence your program :

  • Gear engaged (The same acceleration won't use the same amount of fuel)
  • Type of fuel (petrol, diesel)
  • Car characteristics (weight, aerodynamysn)
  • then what could be the value of ideal acceleration if Gear engaged/ideal gear is predicted through OBD parameters and fuel type is known Petrol? – user3098378 Jun 23 '14 at 10:39
  • @user3098378, I think, regardless of gear, there still should be sensor data on throttle opening, fuel amount, fuel-to-air mixture etc. – theUg Jun 25 '14 at 0:20
  • I agree with you, but you can't link the acceleration of the car to the throttle opening, as it will be completely different wether you're in first or fifth gear. Throttle opening changes the engine rpm, not the wheels rpm, because it depends on the gearbox. – user6233 Jun 25 '14 at 7:12

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