FACTORS AFFECTING KNOCKING IN S.I ENGINE :

FACTORS AFFECTING KNOCKING IN S.I ENGINE :

The various engine variables affecting detonation can be classified under four factors, namely, the temperature factors, density factors, time factors and composition factors.

a) Temperature Factors :

Increasing the temperature of the unburnt mixture by any factor in design or operation will increase the possibility of the knock in the S.I Engine. The temperature of the unburnt mixture is increased by the following factors :

* Raising the compression ratio.

* Supercharging

* Raising the inlet air temperature.

* Raising the coolant Temperature.

* Increasing the load.

* Raising the temperature of the cylinder and combustion chamber walls.

* Advancing the spark timing.

b) Density Factors :

Any factors which increase the density of the charge lend to increase in knocking by providing excess energy release. The following method will increase the possibility of Knock on S.I Engine.

* Increasing the compression ratio.

* Opening the throttle.

* Supercharging the engine.

* Increasing the inlet pressure.

* Advancing the spark timing.

c) Time Factors :

Increasing the flame speed or reducing the duration of the ignition delay period or reducing the time of exposure of the unburnt mixture to auto ignition condition it will tend to reduce knocking. The following factors will increase the possibility of Knocking :

* Increasing flame travel distance : Engine size, combustion chamber size and spark plug position are the three factors governing the flame travel distance.

* Decreasing the turbulence of mixture.

* Decreasing the speed of the engine.

* Increasing the time available for pre flame reaction.

d) Composition Factors :

The properties of fuel and the fuel- air ratio are the primary means for controlling knock, once the compression ratio and engine the dimensions are selected. The probability of knock is increased by the following factors :

* Low Octane Number.

* Lean Mixture of air fuel ratio

* Decreasing atmospheric humidity.

* Low self-ignition Temperature.

* Short Ignition Delay.

Comments

ELECTRICAL COMPARATORS AND ITS WORKING

Electrical Comparators are used as a means of detecting and amplifying small movements of a work contacting elements. An electrical comparator consists essentially of a pick-up head or transducer for converting a displacement into a corresponding change in current and a meter or recorder connected in the circuit to indicate the electrical change, calibrated to show in terms of displacement. Generally, an amplifier is needed to provide the requisite sensitivity and to match the characteristics of different parts of the circuit. Electrical comparators can be classified according to the electrical principle used in the pick-up head. Most of the comparators use either a differential transformer, an inductance bridge, a strain gauge or a capacitor as a means of detecting movement of the gauging element. There are different types of electrical comparators. One kind called an electrolimit gauge is used to check or measure the outside diameter of a roll. The object to be checked is place

THROTTLE GOVERNING OF STEAM TURBINES

Steam Pressure at inlet to a steam turbine is reduced by throttling process to maintain the speed of the turbine constant at part load and hence this method of governing is called "Throttle Governing". Construction : Throttle governing system consists of a centrifugal governor, a lever , an oil pump , a pilot piston , control valve , a relay piston and a throttle valve. The throttle valve is moved by a relay piston. The relay piston is actuated by pilot piston control valve. There are two piston valves covering ports in the pilot piston control valve without any overlap. These piston valves are operated by lubricating oil supplied by a gear pump at 2 to 4 bar. The oil returns to the drain from this chamber. Working : When the turbine works on full rated load, the throttle valve will remain open. When the load is decreased, the energy output of the turbine becomes in excess and the turbine shaft speed increases. Hence, governor sleeve will lift. The upward movement of the

Advantages And Disadvantages Of Air Refrigeration System :

Advantages Of Air Refrigeration : 1. The refrigerant used namely air is cheap and easily available. 2. There is no danger of fire or toxic effects due to leakages. 3. The weight to ton of refrigeration ratio is less as compared to other systems. Disadvantages Of Air Refrigeration : 1. The quantity of Refrigerant used per ton of refrigeration is high as compared to other systems. 2. The COP of the system is very low. Therefore running cost is high. 3. The danger of frosting at the expander valves is more as the air contains moisture content.

Mechinopedia For Mechanical Engineers

Search This Blog