Testing and Performance of Diesel and Petrol Engine

Group Members:1. Muhammad Fahad2. Adeel Ashraf3. Muhammad Irfan4. Huma 5. Mustafa Naqvi

Diesel Engine

• an internal-combustion engine in which heat produced by the compression of air in the cylinder is used to ignite the fuel.

Petrol Engine:

• A petrol engine (known as a gasoline engine in American English) is an internal combustion engine with spark-ignition, designed to run on petrol (gasoline) and similar volatile fuels.

Diesel Engine Under variable Load

Characteristics of IC Engines

1. Brake Thermal Efficiency2. Indicated Thermal Efficiency3. Specific Fuel Consumption4. Mechanical Efficiency5. Volumetric Efficiency 6. Air Fuel Ratio7. Mean Effective Pressure

Brake thermal efficiency

Brake thermal efficiency is defined as break power of a heat

engine as a function of the thermal input from the fuel. It is used to evaluate how well an

engine converts the heat from a fuel to mechanical energy

Indicated thermal efficiency

The thermal efficiency is a dimensionless performance measure of a device that uses thermal energy, for example engine, a steam turbine, a steam engine, a boiler, a furnace, etc, . Thermal efficiency indicates the extent to which the energy added by work is converted to net heat output.

Mechanical efficiency

Mechanical efficiency is the measure of effectiveness of a machine's energy and power that is input into the device into an output that makes force and movement. Mechanical advantage by comparing the input and output force you can find the advantage of a machine

Specific fuel consumption

Thrust specific fuel consumption (TSFC) or sometimes simply specific fuel consumption, SFC, is an engineering term that is used to describe the fuel efficiency of an engine design with respect to thrust output.

Volumetic Efficiency

• Volumetric efficiency in internal combustion engineengineering is defined as the ratio of the mass density of the air-fuel mixture drawn into the cylinder at atmospheric pressure (during the intake stroke) to the mass density of the same volume of air in the intake manifold.

Air Fuel Ratio

• Air–fuel ratio (AFR) is the mass ratio of air to fuel present in a combustion process such as in an internal combustion engine

Mean Effective Pressure

• Mean effective pressure is a quantity relating to the operation of a reciprocating engine and is a valuable measure of an engine's capacity to do work that is independent of engine displacement.

Performance characteristic at variable Speed

• Load and Speed One common way to present the operating characteristics of an internal combustion engine over its full load and speed range is to plot brake specific fuel consumption contours on a graph of brake mean effective pressure versus engine speed.

• Operation of the engine coupled to a dynamometer on a test stand, over its load and speed range, generates the torque and fuel flow-rate data from which such a performance map is derived. The upper envelope of the map is the wide-open-throttle performance curve. Points below this curve define the part-load operating characteristics, While details differ from one engine to another, the overall shapes of these maps for spark-ignition engines are remarkably similar.

• When mean piston speed Sp is used instead of crankshaft speed for the abscissa, the quantitative similarity of such maps over a wide range of engine sizes is more apparent. Maximum bmep occurs in the mid-speed range; the minimum bsfc island is located at a slightly lower speed and at part load. These map characteristics can be understood in terms of variations in volumetric efficiency, gross indicated fuel conversion efficiency and mechanical efficiency.

Torque and Power under variable speed

Performance characteristic at variable load

• Increasing load at constant speed from the minimum bsfc point increases bsfc due to the mixture enrichment required to increase torque as the engine becomes increasingly air-flow limited, Decreasing load at constant speed increases bsfc due to the increased magnitude of friction (due to increased pumping work), the increased relative importance of friction, and increasing importance of heat transfer.

• The effect of speed and load variation on NO and HC emission are can be elaborated as follows. NO concentration increase moderately with increasing speed at constant load. At lower loads, the proportional increase in NO is greater than at higher loads. The residual gas fraction decreases as speed increases, this effect being greater at lower inlet manifold pressures (lighter loads).

• Also, the relative importance of heat transfer per cycle is less as speed increases , which would also be expected to increase NO concentration. With increasing load (at constant speed), NO concentrations also increase. Again, as inlet manifold pressure and load increase, the residual gas fraction decreases also, the relative importance of heat transfer per cycle decreases with increasing load.

The performance of an engine is evaluated on the basis of the following;

• (a) Specific Fuel Consumption. • (b) Measurement of brake Power• (c) Specific Power Output.

Fuel consumption measurement

• Fuel consumption is measured in two ways:

• The fuel consumption of an engine is measured by determining the volume flow in a given time interval and multiplying it by the specific gravity of the fuel which should be measured occasionally to get an accurate value.

• Another method is to measure the time required for consumption of a given mass of fuel

Measurement of brake power

• The brake power measurement involves the determination of the torque and the angular speed of the engine output shaft. The torque measuring device is called a dynamometer.

• Dynamometers can be broadly classified into two main types, power absorption dynamometers and transmission dynamometer.

Types Of Dynamometers

• Absorption Dynamometers • These dynamometers measure and absorb the

power output of the engine to which they are coupled. The power absorbed is usually dissipated as heat by some means. Example of such dynamometers is prony brake, rope brake, hydraulic dynamometer, etc.

• Transmission Dynamometers: In transmission dynamometers, the power is transmitted to the load coupled to the engine after it is indicated on some type of scale. These are also called torque-meters.

Measurement of friction power

• The difference between indicated power and the brake power output of an engine is the friction power.

• Almost invariably, the difference between a good engine and a bad engine is due to difference between their frictional losses.

• The frictional losses are ultimately dissipated to the cooling system (and exhaust) as they appear in the form of frictional heat and this influences the cooling capacity required. Moreover, lower friction means availability of more brake power; hence brake specific fuel consumption is lower.

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