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My relatives bought a diesel car and I found out that their gas mileage is better than my petrol gas mileage. Now, the price of petrol is soaring. Can I increase my mileage to match their gas mileage? My engine and tires are well maintained. I stop the engine at the traffic signal but I still lag behind by miles per gallon.

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3 Answers 3

No. Because you need more Petrol per combustion stroke than Diesel. The air/fuel mixture for Petrol is about 15:1, whereas Diesel starts off at 18:1 and can go even leaner (more air, less fuel). That means that a 2000cc Diesel engine may burn 5ml of fuel per combustion stroke under operating condition X, whereas a 2000cc petrol engine will burn 6.5ml per stroke under the same operating conditions. That means that the petrol engine uses 30% more fuel than the Diesel engine under the same conditions.

Coupled with that, Diesel engines are also optimised for fuel economy through extremely high compression ratios, low-RPM gearing and mild cam profiling. They can do this because Diesel engines produce lots of torque via the combustion properties of Diesel fuel, and can therefore turn higher gears with ease. That means less RPM's is needed. On the other hand, Petrol engines are usually designed to provide a balance of performance and fuel economy. That's because Petrol does not produce as much torque, and therefore we need higher RPM to produce the same number of kiloWatts.

You'll see that a Diesel engine may produce 250Nm of torque and only 100kW of "work". That's because "work" is calculated by multiplying Torque by RPM. A Petrol engine producing 250Nm would usually do 130 to 150 kiloWatts of "work". So the petrol engine "works" harder than a Diesel engine, hence it needs more fuel.

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Here are a few simple ways to increase gas mileage, but not at par with a diesel:

  1. Operate the vehicle at speeds in the range given in the dash board as green color and never run the vehicle at red mark indication.
  2. Keep a minimum payload, take out everything you don't need.
  3. Service the engine periodically.
  4. Run the vehicle at proper gearing and proper speeds.
  5. Keep the car in gear when moving.
  6. Keep your spark plugs clean.
  7. Keep your tires properly inflated.
  8. Avoid running the A/C
  9. Avoid heavy braking, and avoid heavy acceleration.
  10. Maintain bearings and moving parts, grease appropriately.
  11. Clean the air filter often.
  12. Before starting the vehicle check the oil and coolant levels.

Any edits or edit suggestions are most welcome.

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More Tyre pressure give you more mileage. But it will make less friction on road. If your Tyre is too old do not put more pressure , it may cause to blast on ride –  Ullas Prabhakar Oct 30 '12 at 5:13
1  
No, do not over inflate or under inflate your tyres, keep them at the proper inflation recommended by the manufacturer, do not risk your safety for gas milage. –  hillsons Nov 3 '12 at 19:16

The simple answer is:

No. You can't.

To expand a little, both diesel and petrol technologies are continually improving, so you can make incremental changes to your engine in terms of engine management, input air flow etc., and also things like use low rolling resistance tyres etc. But you cannot change the basic fact that your engine is less efficient than his - whether or not one is diesel or petrol.

You can learn to drive more efficiently (see hypermiling for an extreme version of this - some of the techniques may reduce your safety, so be careful)

But if you really want to increase your mileage significantly, you will need to change your engine or your car. Newer cars are generally much more efficient than older cars, and diesel technology currently has a mileage advantage.

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