Fuel injection in ci engines

Fuel injection in ci engines

1. 20-May-21 Topic : Diesel Engine fuel supply system S K Singh Centre for Energy Studies IIT Delhi

2. Fuel Injection System-Objectives The injection system of the compression ignition engine should fulfill the following objectives consistently and precisely: Meter the appropriate quantity of fuel, as demanded by the speed of, and the load on, the engine at the given time. Distribute the metered fuel equally among cylinders in a multi-cylinder engine. Inject the fuel at the correct time (with respect to crank angle) in the cycle. Inject the fuel at the correct rate (per unit time or crank angle degree). Inject the fuel with the correct spray pattern and sufficient atomization as demanded by the design of the combustion chamber, to provide proper penetration also. Begin and end injection sharply without dribbling or after injection. 20-May-21

3. To accomplish these objectives, a number of functional elements are required. These constitute together, the fuel injection system of the engine. These elements are as follows. Pumping elements to transfer the fuel from the tank to the cylinder, along with the associate piping and hardware. Metering elements to measure and supply the fuel at the rate as desired by the speed and load conditions prevailing. Metering controls to adjust the rate of the metering elements for changes in load and speed of the engine. Distributing elements to divide the metered fuel equally among the cylinders in a multi cylinder engine. Timing controls to adjust the start and stop of injection. Mixing elements to atomize and distribute the fuel within the combustion chamber Fuel Injection System-Objectives contd..

4. Function of fuel injection equipment The function of fuel injection equipment is to supply the engine with fuel in qualities exactly metered in proportion to the power required and timed with utmost accuracy , so that the engine will deliver that power within the limits prescribed for fuel consumption, exhaust smoke, noise and exhaust emissions. The fuel must be injected through suitable nozzles at pressures high enough to cause the required degree of atomization in the combustion chamber and to ensure that it mixes with sufficient air for complete combustion in the cycle time available. In multi cylinder engines the periods of injection, the timing and the delivered quantity must be accurately metered to ensure an even balance between the cylinders.

5. For an engine developing 3kW at 60rev/s, of cylinder capacity 0.2 liter the fuel delivery at full load would be approximately 10mm 3 in 1.2ms, repeating this 30 times every second. At no load the quantity will be reduced to approximately to 3mm 3 . In general terms the injection period and the pressure increase with engine size : small direct injection (DI) engines will have a period about 25 degrees crank travel and an injection pressure exceeding 400bar whilst large engines may have periods approximating 40 degrees with pressures in excess of 1000 bar. Function of fuel injection equipment contd..

6. Engines required to meet future limits of exhaust NOx emissions will need shorter injection periods with corresponding higher injection pressures. The equipment for a six cylinder medium-sized high speed turbo charged vehicle engine developing 110kW at 43.3rev/s will have a full load delivery of 65mm 3 with an injection period of approximately 26 degrees crank travel 20-May-21 Function of fuel injection equipment contd..

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12. Indirect Injection system

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14. Indirect Injection system

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16. Classification of Fuel Injection Systems There are two main classifications for fuel-injection systems, namely air injection which had become obsolete but now some interest has been shown by researchers (however very high pressure is required for air) and solid (or airless) injection systems. 20-May-21

17. Classification of Fuel Injection Systems air injection: Fuel is forced in the cylinder by means of compressed air Requires bulky multistage compressor which increases weight and reduces power output so obsolete now a days 20-May-21

18. Classification of Fuel Injection Systems 2. Solid injection: liquid Fuel is injected in the cylinder directly without the aid of compressed air so it is also called airless mechanical injection or solid injection system. Solid injection classification: Individual pump and nozzle system Unit injector system Common Rail system Distributor system 20-May-21

19. The airless, mechanical, or solid injection Individual pump system: This consists of a separate metering and compression pump for each cylinder. Pump may be place close to cylinder or may be arranged in cluster. The HP pump plunger is actuated by a cam, and a produces the final pressure necessary to open the injector valve. Distribution system: This consists of a single pump for compressing the fuel (which may also meter), plus a delivery device for distributing the fuel to the cylinders (which may also meter). A uniform distribution is automatically ensured due to single metering element. Cost is less (2/3 of individual) Common rail system: A single pump for compressing the fuel, plus a metering element for each cylinder.

20. The airless, mechanical, or solid injection 4. Unit Injector system: Pump and injection nozzle are combined in one housing Each cylinder is provided with one of these units Fuel is brought upto the injector by a low pressure pump, where at the proper time, a rocker arm actuates the plunger and thus injects fuel into the cylinder 20-May-21

21. 20-May-21 INDIVIDUAL FEED PUMP

22. 20-May-21 INDIVIDUAL FUEL INJECTION PUMP

23. 20-May-21 INDIVIDUAL FUEL INJECTION PUMP

24. 20-May-21 INDIVIDUAL FUEL INJECTION PUMP WORKING

25. 20-May-21 Some examples: INDIVIDUAL FUEL INJECTION PUMP ASSEMBLY

26. Some examples: 6 cylinder fuel injection pump individual type 20-May-21

27. DISTRIBUTOR PUMP 20-May-21

28. Distributor pump

29. COMMON RAIL FUEL INJECTION PUMP 20-May-21

30. 20-May-21 Common Rail fuel injection system

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33. Spray Delivery Devices - Injector is a spray delivery device. - Injector is responsible for producing the desired spray, with a correct size distribution and velocity. - Injector is very important for the spray behavior. - Once the fuel is injected there is not much one can do to change the spray characteristics.

34. 20-May-21 DIESEL FUEL INJECTOR: Courtesy GM

35. Electronic fuel injector 20-May-21

36. Spray Structure

37. DIFFERENT NOZZLE SHAPES

38. Types of nozzles Single Hole Nozzle : dia = 0.2 mm Pressure = 8 to 10 Mpa Spray cone angle= 15 o 2. Multi Hole Nozzle : dia = 0.2 mm to 0.3 mm Pressure = 18 Mpa Spray cone angle= 20 o 3. Pintle Nozzle : Pressure = 8 to 10 Mpa Spray cone angle= 60 o Advantages: ( i ) avoids dribbling and weak injection and prevents carbon deposits (ii)Used in pre combustion chambers and air cell chambers and high swirl chambers. Pintaux Nozzle: Main hole + Auxilliary holes Advantage : 1.better cold starting as it injects small amount of fuel before Main injection starts. 2. The needle valve does not lift fully at low speed and at This low speed the fuel is supplied by the auxilliary hole.

39. Fuel Filters A low pressure (2.5 bar) transfer pump or fuel feed pump is required to lift the fuel from the tank, to overcome the pressure drop in the filters, and to charge the metering or pressuring unit. Three filters are recommended, namely, A primary stage (a metal- edge filter to remove coarse particles, larger than 25 microns). A secondary stage (a replaceable cloth, paper or lint element to remove fine particles from about 4 to 25 microns) and 3. Final stage (a sealed, non-replaceable element) to remove fine particles that escaped the secondary stage.

40. Latest models of diesel injectors (for Information)

41. Modern injectors Contd … for information

42. 20-May-21 Some modern injectors:

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