Fuel Injection MCQ Quiz - Objective Question with Answer for Fuel Injection - Download Free PDF

Explanation:

Fuel Injectors:

• The function of the fuel injector is to deliver finely atomized fuel under high pressure to the combustion chamber for the engine.
• In a diesel engine, the injector pressure is 100 to 120 bar.
• The diesel injector is tested by a pressure testing gauge.
• Pressure testing gauges are industrial equipment used for measuring pressure fluctuations. Generally, they are installed on the fluid transmission lines in industrial supply systems.
• All component parts of the injector are carried in a nozzle holder.
• The main part of the injector is the nozzle comprising the nozzle body and nozzle valve.
• The nozzle body and needle valve are fabricated from alloy steel.
• They are thoroughly machined and have a high surface hardness necessary for operation in conditions of high temperatures and elevated pressures.
• The bore in the nozzle body and the nozzle needle valve are lapped to a close tolerance and are a matched set, so that neither the nozzle body nor the needle valve may be replaced individually.
• The needle valve is pressed against a conical seat in the nozzle body by a spring acting through the intermediary of the stem.
• The spring pressure is adjusted by adjusting the screw.
• The adjusting screw is screwed into the bottom of the injector spring cap nut which in turn is screwed into the nozzle holder.
• A lock nut is used to prevent the adjusting screw from unscrewing spontaneously.
• The screw is covered by a nozzle holder cap nut provided with a threaded hole to connect the leak-off pipe through which the leak-off fuel (used to lubricate the nozzle valve) filling the pressure spring and adjusting screw area is returned to the fuel tank or the secondary fuel filter.
• In operation, fuel from the injection pump enters the pressure chamber (gallery) in the nozzle body through a supply passage and a high-pressure pipe.
• When the fuel pressure in the pressure chamber becomes so high that the force acting on the pressure taper of the needle valve from below exceeds the set spring force on the stem, the needle valve lifts off its seat and comes to rest with its upper shoulder against the face of the nozzle holder.
• Fuel is then forced out of the nozzle spray holes into the combustion chamber in a spray pattern which depends on the type of nozzle used.

 

Explanation:

Boiler accessories 

• These are those components which are installed either inside or outside the boiler to increase the efficiency of the plant and to help in the proper working of the plant.
• Various boiler accessories are:
  1. Air Preheater
  2. Economizer
  3. Super-heater
  4. Feed Pump
  5. Injector

The correct path of flue gases from boiler furnace to chimney is:

Boiler → Superheater → Economiser → Air preheater → ID fan → Chimney

• Superheaters: It is used to dry the wet steam and raise the temperature of the steam above its saturation temperature. It is generally placed in the path of the furnace gases so as to utilize the heat from the hot flue gases.
• Economizer: It is also known as a feedwater heater. It is a device in which the waste heat of the flue gases is utilized for heating the feed water.
• Air Preheater: It is used to increase the temperature of the air before it enters the furnace. It is generally placed after the economizer; so that the flue gases pass through the economizer and then to the air preheater.
• Injector: It is a device used to feed the water into the boiler. It is usually employed when space is less and a feedwater pump cannot be employed. It is used for vertical and locomotive boilers. Steam from the boiler is accelerated by a nozzle and as the pressure at the exit is low, therefore it enters into feedwater.

Explanation:

Air-blast injection system:

• In the air blast injection system, a high-pressure air blast drives the fuel at a very high velocity into the cylinder where it is mixed with the compressed air in the cylinder and ignites.
• Air injection fuel injection systems were originally used in large stationary and marine engines and are now seldom used.
• In an air-blast injection system, a compressor and a storage tank supply air at a pressure much higher than that existing in the engine cylinder, as means of injecting and atomizing the fuel oil.
• The air blast engine is too heavy and bulky, the compressor uses 10% of the output of the engine.
• Therefore the efficiency is also considerably low of the air-blast injection system.
• An air blast injection system consists of the following units:
• An air compressor for providing an adequate supply of air at a pressure several hundred pounds higher than the engine compression pressure.
• High-pressure air bottles of sufficient capacity to provide a steady flow of high-pressure air for injection as well as for engine starting.
• Atomizers in each engine cylinder for injecting the metered fuel by blasts of high-pressure air into the combustion chamber in an adequately atomized and disbursed state.
• The cam mechanism is used for timing and lifting the atomizer valve to control the injection process.
• A fuel pump is used to meter and deliver to each atomizer the proper quantity of fuel in accordance with engine requirements of speed and load.

Mechanical injection:

• In a mechanical fuel injection system, fuel is forced in from a mechanical fuel injection pump through injectors.
• There are of two types:
  1. Low-pressure fuel supply system
  2. Metering injection system

Explanation:

Fuel feed pump:

• A feed pump is usually mounted on the F.I.P. (fuel injection pump) and is driven by the camshaft of the F.I.P.
• It sucks fuel from the fuel tank and supplies it to fuel filters.
• The fuel feed pump consists of a barrel, a plunger, a plunger return spring, a spindle, a roller tappet, suction and delivery valves, a hand primer, and a pre-filter.
• The feed pump plunger (1) is driven by the cam (2) provided on the F.I.P. camshaft (3).
• The roller of a feed pump is operated by an eccentric cam of a FIP camshaft.
• When the plunger moves “downwards” by means of the roller tappet (4) and pressure spindle (5) a portion of the fuel present in the suction chamber (6) is delivered through the pressure valve (7) to the pressure chamber (8) and the plunger spring (9) compressed in an intermediate stroke.
• Toward the end of this stroke, the spring-loaded pressure valve closes again.
• As soon as the cam or eccentric has passed its maximum stroke, the plunger, pressure spindle, and roller tappet move “upward” due to the pressure exercised by the plunger spring.
• A portion of the fuel present in the pressure chamber is thereby delivered to the fuel injection pump through a filter.
• However, fuel is sucked simultaneously from the fuel tank to the suction chamber through the primary filter provided in the feed pump and suction valve (10).

 

Explanation:

Governors:

• A mechanism used to control the speed of an engine is called the governor.
• The governor is a device for holding any speed steady between idling and maximum speed.
• The fuel injection pump operates in conjunction with a governor, which is required to control the injected quantity of fuel so that the engine neither stalls when idling nor exceeds the maximum speed for which it is designed.

The following types of Governors are used:

• Mechanical
• Pneumatic
• Servo
• Hydraulic

Additional InformationSpeedometer:

• A speedometer or a speed meter is a gauge that measures and displays the instantaneous speed of a vehicle.
• The unit in which the display is shown is in Km/hr.
• There are both analog and digital meters are available nowadays.

Odometer:

• Odometer is an instrument that indicates the distance traveled by a vehicle, such as a motorcycle or motor vehicle automobile.
• The device may be electronic, mechanical, or a combination of both.
• It is also called a trip meter in case of short trips of every ride.
• The distance mentioned in the odometer is generally in km.

Explanation: 

Jerk pump injection system:

• The jerk pump controlled system has a single reciprocating type pump for each fuel injection.
• The pump is separately mounted on the engine block.
• Jerk pumps belong to the stationary category.
• The pump is driven by an accessory shaft. The pump plunger has a constant stroke with a variable effective stroke.
• The injector is connected to the pump by suitable tubing.
• The injector is opened by lifting the needle valve automatically by fuel pressure.
• When the fuel pressure in the system falls below a certain value, the spring-loaded injector needle valve terminates fuel injection.

 

The hand priming device is screwed into the feed pump above the suction valve. When the engine is at rest, with the aid of the hand priming device fuel can be pumped from the fuel tank through the filter to the F.I.P.

The common rail consists of fuel tank, electrical fuel pump (low pressure) placed inside the fuel tank. It develops pressure up to 6 bar and supplies to the high-pressure fuel pump (CRDI) through fuel filter and water separator. The high-pressure fuel pump develops pressure from 200 to 2000 bar and supplies to the common rail and common rail fuel injectors inject fuel into the combustion chamber.

Injectors: Injectors are provided to atomise the fuel into engine cylinder. This is done to achieve complete combustion.

Muffler: The muffler reduces the engine exhaust noise.

Spark Plug: It is used to provide spark in the SI engines to ignite the air fuel mixture.

Multi Point Fuel Injection (MPFI) is an intelligent system and is more efficient as compared to the carburettor. It is a type of petrol injection technique used in SI engines in place of carburettors. Due to MPFI, there is significant improvement in the engine efficiency

Explanation

Common Rail Direct Injection (CRDI):

• The common rail fuel system consists of fuel tanks, fuel pumps, common rail, pressure regulators, injectors, and sensors.
• The electrical fuel pump (low pressure) is placed inside the fuel tank.
• It develops pressure up to 6 bar and supplies to the high-pressure fuel pump (CRDI) through a fuel filter and water separator.
• The high-pressure fuel pump develops a pressure of 200 to 2000 bar and supplies to the common rail and common rail to fuel injectors inject fuel into the combustion chamber.
• Fuel injectors are operated by ECM through a solenoid valve.
• Common rail consists of a fuel pressure regulator rail pressure sensor and the fuel pressure regulator supplies the excess amount of fuel to the fuel tank (< 1 bar pressure).
• The common rail pressure sensor sends information to ECM/EDC, the existing pressure in the common rail will control the RPM of the fuel pump.
• Common rail will distribute the fuel to all the cylinders with equal pressure, then all cylinders will develop uniform power, which will reduce the vibration and noise of the engine.
• The order that best describes how the fuel feed system's components are arranged in common rail direct injection:
  • ​Fuel Tank, Low-Pressure Fuel Pump, Fuel Filter, High-Pressure Fuel Pump, Common Rail, Injector & Engine

 

Explanation:

Unit injector system:

• A unit injector (UI) is a high-pressure integrated direct fuel injection system for diesel engines, combining the injector nozzle and the injection pump in a single component.
• The plunger pump used is usually driven by a shared camshaft. In a unit injector, the device is usually lubricated and coole8d by the fuel itself.
• The high-pressure injection delivers power and fuel consumption benefits over earlier lower-pressure fuel injection by injecting fuel as a larger number of smaller droplets, giving a much higher ratio of surface area to volume.
• This provides improved vaporization from the surface of the fuel droplets and so more efficient combining of atmospheric oxygen with vaporized fuel, delivering more complete and cleaner combustion.
• Design of the unit injector eliminates the need for high-pressure fuel pipes, and with that their associated failures, as well as allows for much higher injection pressure to occur.
• The unit injector system allows accurate injection timing and amount control as in the common rail system.
• The unit injector is fitted into the engine cylinder head, where the fuel is supplied via integral ducts machined directly into the cylinder head.
• Each injector has its own pumping element, and in the case of electronic control, a fuel solenoid valve as well.
• The fuel system is divided into the low-pressure (< 5 bar) fuel supply system, and the high-pressure injection system (< 2000 bar).

Technical characteristics:

• The special feature of the unit injector system is that an individual pump is assigned to each cylinder
• The pump and nozzle are therefore combined in a compact assembly which is installed directly in the cylinder head
• The unit injector system enables high injection pressures of up to 2,200 bar.

Explanation: 

Jerk pump injection system:

• The jerk pump controlled system has a single reciprocating type pump for each fuel injection.
• The pump is separately mounted on the engine block.
• Jerk pumps belong to the stationary category.
• The pump is driven by an accessory shaft. The pump plunger has a constant stroke with a variable effective stroke.
• The injector is connected to the pump by suitable tubing.
• The injector is opened by lifting the needle valve automatically by fuel pressure.
• When the fuel pressure in the system falls below a certain value, the spring-loaded injector needle valve terminates fuel injection.

 

The hand priming device is screwed into the feed pump above the suction valve. When the engine is at rest, with the aid of the hand priming device fuel can be pumped from the fuel tank through the filter to the F.I.P.

The common rail consists of fuel tank, electrical fuel pump (low pressure) placed inside the fuel tank. It develops pressure up to 6 bar and supplies to the high-pressure fuel pump (CRDI) through fuel filter and water separator. The high-pressure fuel pump develops pressure from 200 to 2000 bar and supplies to the common rail and common rail fuel injectors inject fuel into the combustion chamber.