Engine Tuning to Improve Fuel Consumption

Engine tuning to improve fuel consumption is important in all applications of the internal combustion engine. This may require adjustment, modification or fundamental design changes of the internal combustion engine to yield better fuel economy.

In a normal internal combustion engine 23% of the energy that comes in as fuel appears as useable output.

In terms of the energy input, 35% appears as Indicated Power, 30% goes into the cooling system and 35% goes down the exhaust.

The losses in the engine:

  • Air Pumping (6%)
  • Seals (0.5%)
  • Bearings (1%)
  • Valve Train (1.3%)
  • Piston Assembly (2.8%)
    • Viscous Loss (1.35%)
    • Friction Forces (0.95%)
    • Blowby (0.5%)
  • Other Engine Friction (0.4%)

Roughly 10% of the energy input is lost in friction in the engine.

Engine efficiency for thermal engines is the relationship between the total energy contained in the fuel, and the amount of energy used to perform useful work.

Brake Mean Effective Pressure

This is the average effective cylinder pressure that does useful work calculated from the brake horse power.

The work accomplished during one engine cycle divided by the engine swept volume. It is essentially the engine torque normalized by the engine displacement. The word ′brake′ denotes the actual torque/power available at the engine flywheel as measured on a dynamometer. Thus, BMEP is a measure of the useful power output of the engine.

Brake Power

The engine power as measured at the output shaft.

Brake Thermal Efficiency

The ratio Brake Power to Heat of Fuel.

Indicated Mean Effective Pressure

During the cycle of an engine useful work is only done on the power stroke. By measuring the cylinder pressure through a cycle it is possible to calculate the average pressure that is useful. This is the Indicated Mean Effective Pressure.

Indicated Power

The power developed in the engine cylinder, as calculated from an indicator diagram.

Mechanical Efficiency

The mechanical efficiency takes into account friction losses in the bearings, piston sliding losses and valvetrain losses. The ratio of Brake Power to Indicated Power is the mechanical efficiency.

Power Lost to Friction

This can be calculated from the difference between Indicated Power and Brake Power.

Engine tuning to improve fuel consumption is a key aspect of a new engine design and when using an existing engine in a new vehicle or application.


  1. George Fenske, Robert Erck, Layo Ajayi, Ali Erdemir and Osman Eryilmaz, “Parasitic Energy Loss Mechanisms Impact on Vehicle System Efficiency”, Argonne National Laboratory

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