Skip to main content

Choking device




Starting an engine in cold weather is somewhat difficult. Choking device makes engine starting easier. The choke valve is butterfly valve, similar to the throttle valve. This valve is situated between the air intake and the venture.
At the time of starting, the choke valve is turned to close almost the inlet passage. This is called choking. Then, during suction stroke, a greater depression is created in the inlet passage and is felt on the fuel jet which is situated at the throat of the venture. This causes more fuel to be ejected by the fuel jet. Choking restricts airflow and provides an over supply of fuel. It should be remembered that only the lighter fractions of the supplied fuel evaporate at lower temperatures and form a combustible mixture in the cylinder.
During initial cranking of the engine, the choke valve is almost completely closed. Once the engine fires consistently, the choke valve is opened slightly to keep the engine running. As the engine warms up to its normal temperature, the choke valve is opened gradually to its full extent. At all other times of engine operation, the choke valve is kept wide open. Thus the inlet passage is unrestricted.

The choke valve may be operated either manually or automatically. Manual choke operation is usually effected by a flexible cable connected to a knob in the dash board/instrument panel. Automatic choking is accomplished by a thermostatic element. The tension of the thermostat spring keeps the choke valve in a nearly closed position. As soon as the engine begins to operate, the exhaust gases heat the thermostat casing. This decreases in the tension of the spring and causes the choke valve to open to wide open position.
During choking, only the lighter fractions of the supplied fuel evaporate and form the combustible mixture in the cylinder. The unvapourized heavier fractions of the fuel mxi with lubricating oil film on the cylinder wall. The contaminated lubricating oil may run down into the crankcase as the piston rings scrape the oil. Thus, the crankcase oil gets diluted. This lowers the lubricating characteristics of the oil and may cause greater wear of the engine parts. It is evident, that during choking, fuel is wasted. Hence, choking should be done only when the engine fails to start and should be limited to the minimum period necessary to realize starting.
Unloader or dechoker If, for any reason during starting period, the engine is flooded, it becomes necessary to clear the excessive gasoline out of the intake manifold. This is accomplished by an arrangement of the throttle lever and chokes lingage. In one arrangement depressing the accelerator pedal to the floorboard forces the choke to open sufficiently to allow the engine to clean out the intake manifold. This device is called unloader or dechoker.
Saurabh_savy

Labels:

Comments

Post a Comment

Popular posts from this blog

IC Engine

You all are aware from this word IC Engine, but still don't know what exactly it is. "An  internal combustion engine  (ICE) is a heat  engine  where the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit." The  internal combustion engine  is an engine in which the burning of a fuel occurs in a confined space called a combustion chamber. This exothermic reaction of a fuel with an oxidizer creates gases of high temperature and pressure, which are permitted to expand. The defining feature of an internal combustion engine is that useful work is performed by the expanding hot gases acting directly to cause movement, for example by acting on pistons, rotors, or even by pressing on and moving the entire engine itself. This contrasts with external combustion engines, such as steam engines, which use the combustion process to heat ...
Post a Comment
Read more

Competitions for mechanical engineers

There are various competitions in which you can participate during your graduation. SAE (society of automative engineers) organize three major events every year :  1. BAJA SAE- design and build an all terrain vehicle 2. SUPRA SAE- design and build a formula type race car 3. EffiCycle- design and build a hybrid cycle ASME  ( american society of mechanical engineers) organize human powered vehicle challenge HPVC. ISNE - It organizes go karting championship. If you have interest in automobiles then these competitions will definitely helps you to improve your skills.I was participated in SUPRA SAE (2016).It was a cool experience for me and helps me to improve my basic knowledge. Please like ,share and comment. Subscribe for more updates. Saurabh_savy 
Post a Comment
Read more

Working of air conditioner

Air conditioners and refrigerators work the same way. Instead of cooling just the small, insulated space inside of a refrigerator, an air conditioner cools a room, a whole house, or an entire business. Air conditioners use chemicals that easily convert from a gas to a liquid and back again. This chemical is used to transfer heat from the air inside of a home to the outside air. The machine has three main parts. They are a compressor, a condenser and an evaporator. The compressor and condenser are usually located on the outside air portion of the air conditioner. The evaporator is located on the inside the house, sometimes as part of a furnace. That's the part that heats your house. The working fluid arrives at the compressor as a cool, low-pressure gas. The compressor squeezes the fluid. This packs the molecule of the fluid closer together. The closer the molecules are together, the higher its energy and its temperature. The working fluid leaves the compresso...
Post a Comment
Read more