Skip to main content

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.



Labels:

Comments

Post a Comment

Popular posts from this blog

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. 
Post a Comment
Read more

SIMPLE CARBURETOR - CONSTRUCTION AND WORKING

CONSTRUCTION OF SIMPLE CARBURETOR :  The main Components of Simple Carburetor are : Float Chamber, float, nozzle, venturi, throttle valve, inlet valve, and metering jet . In the float chamber, a constant level of petrol is maintained by the float and a needle valve.  The float chamber is ventilated to atmosphere.  This is used to maintain atmospheric pressure inside the chamber. The float which is normally a metallic hollow cylinder rises and closes the inlet valve as the fuel level in the float chamber increases to certain level. The mixing chamber contains venturi, nozzle and throttle valve. The venturi tube is fitted with the inlet  manifold. This tube has a narrow opening called venturi. A nozzle is provided just below the centre of this venturi. The nozzle keeps the same level of petrol as that of the level in the float chamber. The mixing chamber has two butterfly valves.  One is to allow air into the mixing chamber known as choke valve. The other is to al...
Post a Comment
Read more

MELTING FURNACES FOR FERROUS METALS : CUPOLA AND ITS WORKING

Various types of melting furnaces are used in different foundry shops, depending upon the quantity of metal to be melted at a time, and the nature of work that is carried out in the shop.  The primary objective in cupola is to produce iron of desired composition, temperature and properties at the required rate in the most economical manner. Besides, this furnace has many distinct advantages over the other types, e.g., simplicity of operation, continuity of production, and increased output coupled with a high degree of efficiency.  Description Of a Cupola : The Cupola Furnace consists of a vertical, cylindrical steel sheet, 6 to 12 mm thick, and lined inside with acid refractory bricks or acid tamping clay. The refractory bricks or the tamping clay used consist of  silicon oxide acid (SiO2) and alumina (Al2O3). The lining is generally thicker in the lower where the temperatures encountered are higher than in the upper region. The shell is mounted either on a brick work fo...
Post a Comment
Read more