types of fuel injection system and nozzles
- 1. Unit-4 Combustion in C.I. Engines
- 2. Introduction to Fuel Injection System • Engine Performance i.e. Power Output, economy is greatly dependent on the effectiveness of the fuel injection system. • In case of carburetion, fuel is atomized by processes relying on the air speed greater than fuel speed at the fuel nozzle whereas in Fuel-injection the fuel speed at the point of delivery is greater than the air speed to atomize the fuel. • In a fuel injection system, the amount of fuel delivered into the air stream going to the engine is controlled by a pump which forces the fuel under pressure.
- 3. Requirements of Injection Systems • The fuel injection should occur at the correct moment. • It should supply the fuel in correct quantity as required by the varying engine loads. • The injected fuel must be broken into very fine droplets. • The spray pattern should ensure rapid mixing of fuel and air. • It should supply equal quantities of metered fuel to all the cylinders in a multi cylinder engines • The beginning and the end of injection should be sharp
- 4. Elements of Fuel Injection System • Pumping elements: to supply fuel from fuel tank to cylinder. • Metering elements: to meter fuel supply as per load and speed. • Distribution elements: to divide the metered fuel equally among the cylinders. • Timing controls: to adjust the start and the stop of injection. • Mixing elements: to atomize and distribute the fuel within the combustion chamber.
- 5. Types of Injection system • Air (Blast) Injection System: In air blast injection system, fuel is forced into the cylinder by means of compressed air. • This method is capable of producing better atomization and penetration of fuel resulting in higher brake mean effective pressure. • This system is little used universally at present, because it requires a multistage air compressor, which increases engine weight and reduces brake power.
- 6. Types of Injection system (Contd.) • Solid Injection System: In solid injection, the liquid fuel is injected directly into the combustion chamber without the aid of compressed air. Hence, it is termed as airless mechanical injection or solid injection. • Every solid injection system must have – a pressuring unit (the pump)and – an atomizing unit (the injector).
- 7. Types of Solid Injection system • Depending upon the location of the pumps and injectors, and the manner of their operations, solid injection systems may be further classified as follows: – Common Rail System – Unit Injection System – Individual Pump and Nozzle System – Distributor System
- 8. Fuel Supply System In C.I. Engines
- 9. Common Rail System In this system, a high-pressure pump supplies fuel to a fuel header as shown. The high-pressure in the header forces the fuel to each of the nozzles located in the cylinders. At the proper time, a mechanically operated (by means of push rod and rocker arm) valve allows the fuel to enter the cylinder through nozzle.
- 10. Unit Injection System Here, the pump and nozzle are combined in one housing. Each cylinder is provided with one of these unit injectors. Fuel is brought up to the injector by a low-pressure pump, where at the proper time, a rocker arm activates the plunger and thus injects the fuel into the cylinder. The quantity of fuel injected is controlled by the effective stroke of the plunger.
- 11. Individual Pump and Nozzle System Separate Pumps Pump in Clusters
- 12. Individual Pump and Nozzle System • In this system, each cylinder is provided with one pump and one injector. • This type differs from the unit injector in that the pump and injector are separated from each other, i.e., the injector is located on the cylinder, while the pump is placed on the side of the engine. • Each pump may be placed close to the cylinder, or may be arranged in a cluster. • The high-pressure pump plunger is actuated by a cam, and produces the fuel pressure necessary to open the injector valve at the correct time. • The quantity of fuel injected is again controlled by the effective stroke of the plunger
- 13. Distributor System Here, the pump which pressurizes the fuel also meters and times it. The fuel pump after metering the required quantity of fuel supplies it to a rotating distributor at the correct time for supply to each cylinder. Since there is one metering element in each pump, a uniform distribution is ensured.
- 14. Injection Pump • The main objective of the fuel injection pump is to deliver accurately a metered quantity of fuel under high pressure at the correct instant to the injector fitted on each cylinder. • Two types of pumps are generally used viz., jerk type and distributor type. • Fuel delivered by a pump increases with speed while the opposite is true about the air intake. This results in over fueling at higher speeds. At low speeds, the engine tends to stall due to insufficiency of fuel. • To overcome this, injector pump governors are generally used. Two types of governors are found in applications viz., (a) mechanical governor and (b) pneumatic governor.
- 15. Fuel Injector • Quick and complete combustion is ensured by a well designed fuel injector. By atomizing the fuel into very fine droplets, it increases the surface area of the droplets resulting in better mixing and subsequent combustion. Atomization is done by forcing the fuel through a small orifice under high pressure. An injector assembly consists of the following components. – a needle valve – a compression spring – a nozzle – an injector body
- 16. Operation of Fuel Injector • Fuel is injected by a pump. The pump exerts sufficient pressure/force that lifts the nozzle valve. • The spring tension and hence the valve operating pressure is controlled by adjusting the screw at the top. • When the nozzle valve is lifted up, fuel is sprayed into the combustion chamber. As the fuel supply is exhausted, the spring pushes the valve back on its seat.
- 17. Nozzle • The nozzle sprays the liquid fuel. The functions of the nozzle are: (a) atomization, (b) distribution of fuel to the required area, (c) non-impingement on the walls, and (d) no dribbling. • Note: The fuel striking on the walls decomposes and produces carbon deposits. This causes smoky exhaust and increases fuel consumption. • Note: High injection pressure allows better dispersion and penetration into the combustion chamber. High air density in the cylinder gives high resistance to the droplets. This further causes dispersion.
- 18. Types of Nozzles
- 19. Single Hole Nozzle The single hole nozzle requires a high injection pressure and this type of nozzle has a tendency to dribble. The spray cone angle is usually narrow, and this gives poor mixing unless the velocity is high.
- 20. Pintle Nozzle The pintle nozzle has been developed to avoid weak injection and dribbling. The spindle is provided with a pintle capable of protruding in and out. Pintle nozzle results in good atomization and reduced penetration.
- 21. Multi-Hole Nozzle A multi-hole nozzle, where the number of holes may vary from 4 to 18, allows a proper mixing of air and fuel. The advantage lies with the ability to distribute the fuel properly even with lower air motion within the chamber.
- 22. Pintaux Nozzle • The pintaux nozzle is a pintle nozzle with an auxiliary hole drilled into the nozzle body. At low speeds, the needle valve does not lift fully and most of the fuel is injected through this auxiliary hole