Brake specific fuel consumption

The specific fuel consumption is a measure of the efficiency of an internal combustion engine. Defined it as the ratio between fuel consumption per unit time and the mechanical power delivered. In jet and rocket engines, there is a similar code. This is described in the article Specific Impulse.

Unit of specific fuel consumption

The unit of specific fuel consumption is usually expressed in g / kWh.

Specific fuel consumption as a benchmark

Internal combustion engines could only be compared with each other on the basis of the specific fuel consumption if the power measurement is carried out according to the same standards, and the fuel per unit weight have the same calorific value. In the article horsepower is shown that different measurement methods for the determination of engine power are possible.

Conversion to Anglo-American units

In the Anglo-American system of measurement is the specific fuel consumption in internal combustion engines, which deliver the power to a shaft as " Brake Specific Fuel Consumption " means ( Abbr: BSFC ) and in lbs / (hp · h) specified.

Conversion of

• G / kWh according to lbs / (hp · h) → 1 g / kWh = 0.001644 lb / (hp · h)
• Lbs / (hp · h ) to g / kWh → 1 lb / (hp · h) = 608 277 g / kWh

Specific fuel consumption and efficiency

The efficiency of an internal combustion engine relating to the heating value of the fuel rather than its (higher) energy value. The calorific value is usually given in kJ / kg or kWh / kg. The conversion is: 1 kWh = 3600 kJ. Are specific fuel consumption and calorific value of the fuel is known, then, the efficiency calculated as follows:

Example: In a diesel engine, a specific fuel consumption is determined ( in a certain operating point ) of 206 g / kWh. The heating value of the spent diesel fuel is about 11.8 kWh / kg. The efficiency is calculated as follows:

It should be noted that the usual fuels consist of fuel blends and the calorific values ​​therefore are not constant. Examples are winter diesel, summer diesel and petrol with varying degrees of ethanol blends.

Maps the specific fuel consumption

The specific fuel consumption - and thus the efficiency - is not a constant value but depends on the operating condition of the engine. Depending on the engine speed and load, different values ​​arise. However, often only a single value is specified. This value is - if no further explanation follows - the " best value ", ie the maximum achievable optimum.

Much more meaningful is a characteristic diagram of the specific fuel consumption. This is also referred to as " mussel diagram ". From this diagram, all other values ​​occurring at full load and at part load can be next to the " best point " read.

A particular significance of these characteristic fields for the design and control of manual transmissions. By suitable choice of the gear ratio, the engine speed can be set so that the respective optimum consumption is achieved.

• Fuel technology