AICE-Unit 2
- 1. COMPRESSION IGNITION ENGINES Diesel Fuel Injection Systems - Stages of combustion – Knocking – Factors affecting knock – Direct and Indirect injection systems – Combustion chambers – Fuel Spray behaviour – Spray structure and spray penetration – Air motion - Introduction to Turbocharging.
- 2. The main purpose of the fuel injection system is to deliver fuel into the cylinders of an engine. In order for the engine to effectively make use of this fuel: Fuel must be injected at the proper time, that is, the injection timing must be controlled and The correct amount of fuel must be delivered to meet power requirement, that is, injection metering must be controlled.
- 3. Many specialized concepts and terms are used to describe the components and the operation of diesel fuel injection systems. Nozzle Nozzle Injector commonly refers to the nozzle holder and nozzle assembly holder or injector body Start of injection (SOI) or injection timing Start of delivery End of injection (EOI) Injected fuel quantity Injection duration
- 4. Injection pattern Multiple injection event Low pressure side components—These components serve to safely and reliably deliver fuel from the tank to the fuel injection system. Low pressure side components include the fuel tank, fuel supply pump and the fuel filter. High pressure side components—Components that create high pressures, meter and deliver the fuel to the combustion chamber. They include the high pressure pump the fuel injector and fuel injection nozzle. Some systems may also include an accumulator.
- 5. Stages of combustion in CI engine In the Compression Ignition Engine, the combustion process will be completed in the four stages in an actual engine. Ignition Lag Rapid Combustion Controlled Combustion After Burning
- 7. Ignition Lag The time interval between the injection of the fuel and the start of the self-ignition of the fuel is known as ignition lag or Ignition delay. It is also referred to as the preparation phase The fuel does not ignite immediately upon the injection of fuel into the combustion chamber. There will be a definitely a certain amount of period will be delayed between the first droplet of the fuel injected into the combustion chamber and the time at which it starts the burning phase.
- 8. There are two chances that can cause the ignition delay. Physical delay and chemical delay. Physical delay due to the complete injection of fuel, atomisation, vaporization and mixing of air and fuel and raised to its self-ignition point. The chemical delay due to the burning slowly starts and then accelerates until the complete ignition takes place.
- 9. Rapid Combustion The period of rapid combustion also known as the uncontrolled combustion. This rapid combustion will starts right After the ignition delay period ends. During this period the heat release is maximum. The pressure released during this period depends on the ignition delay period. If the ignition delay period is more, then the pressure rise is more due to the more fuel will be accumulated during the delay period.
- 10. Controlled Combustion The rapid combustion followed by the third stage called the controlled combustion. During the rapid combustion, the cycle reaches its maximum pressure and the temperature. Which means the fuel droplets injected into the combustion chamber during the rapid combustion stage will burn faster with reduced ignition delay as soon as they find the necessary oxygen and any further pressure rise is controlled by the injection
- 11. At the point at where it reaches the maximum cycle pressure the rapid combustion ends and the controlled combustion starts. The period of the controlled combustion is assumed to end at the maximum cycle temperature.
- 12. After Burning The combustion process will not stop right after the completion of the injection process. The unburnt particles left in the combustion particles will start burning as soon as they get in contact with the oxygen. This process continued for a certain period amount of time called the after burning.
- 13. Knocking, in an internal-combustion engine, sharp sounds caused by premature combustion of part of the compressed air-fuel mixture in the cylinder. In a properly functioning engine, the charge burns with the flame front progressing smoothly from the point of ignition across the combustion chamber. However, at high compression ratios, depending on the composition of the fuel, some of the charge may spontaneously ignite ahead of the flame front and burn in an uncontrolled manner, producing intense high- frequency pressure waves. These pressure waves force parts of the engine to vibrate, which produces an audible knock.
- 14. Causes of Knocking 1. Low Quality Fuel 2. Carbon Deposits in the Cylinder Wall, and 3. Advanced or Delayed Sparking 4. Improper fuel supply.
- 15. Knocking in CI Engine
- 16. Knocking in SI and CI Engine
- 17. Normal Combustion Under ideal conditions the common internal combustion engine burns the fuel/air mixture in the cylinder in an orderly and controlled fashion.
- 19. Factors affecting Delay period
- 20. Factors affecting Delay period
- 21. Factors affecting Delay period
- 22. Factors affecting Delay period
- 23. Factors affecting Delay period
- 24. Reducing Knocking in SI and CI engine
- 25. The main reason of knocking in a CI engine is the ignition delay, after the compression stroke has ended. Following parameters will minimize knocking in CI engines. Compression ratio: high Self ignition temp: low Delay period: less Inlet temp and pressure: high Combustion chamber temp: high RPM : low Engine size : small Cetane Rating: High
- 26. Combustion Chamber in CI engine 1. Direct Injection type 2. Indirect Injection type 1. Direct Injection Type. • Shallow depth Chamber • Hemispherical Chamber • Cylindrical Chamber • Toroidal Chamber
- 27. Direct Injection Type Shallow depth Chamber Hemispherical Chamber
- 28. Direct Injection Type Cylindrical Chamber Toroidal Chamber
- 29. 2. Indirect Injection Type.
- 30. Indirect Injection Type 1. Swirl Chamber
- 31. Indirect Injection Type 2. Precombustion Chamber
- 32. Indirect Injection Type 3. Air-Cell Combustion Chamber
- 33. A significant difference between a turbocharged diesel engine and a traditional naturally aspirated gasoline engine is the air entering a diesel engine is compressed before the fuel is injected. This is where the turbocharger is critical to the power output and efficiency of the diesel engine.
- 34. It is the job of the turbocharger to compress more air flowing into the engine’s cylinder. When air is compressed the oxygen molecules are packed closer together. This increase in air means that more fuel can be added for the same size naturally aspirated engine. This then generates increased mechanical power and overall efficiency improvement of the combustion process. Therefore, the engine size can be reduced for a turbocharged engine leading to better packaging, weight saving benefits and overall improved fuel economy.
- 35. Turbo charging 1. Exhaust Turbo charging of Single cylinder engine.
- 36. Turbo charging 2. Exhaust Turbo charging of a V type engine.
- 40. Spray Formation
- 41. The spray characteristics of fuel mainly depend on the fuel injection pressure, density, viscosity, ambient pressure, and temperature. Among these parameters, fuel injection pressure significantly affects the spray structure
- 44. Fuel Spray
- 49. AIR MOTION WITHIN THE CYLINDER The air motion inside the cylinder greatly influences the performance of diesel engines. It is one of the major factors that controls the fuel-air mixing in diesel engines. Air- fuel mixing influences combustion, performance and emission level in the engine. The air motion inside the cylinder mainly depends on manifold design, inlet and exhaust valve profile and combustion chamber configuration. The initial in-cylinder intake flow pattern is set up by the intake process, and then it is modified during the compression process. The shape of the bowl in the piston and the intake system, control the turbulence level and air-fuel mixing of the DI diesel engine. The variation of shape of intake system, shape of piston cavity, etc. lead to a change in the flow field inside the engine.
- 50. EFFECTS OF AIR MOTION • Atomizes the injected fuel into droplets of different sizes. • Distributes the fuel droplets uniformly in the air charge. • Mixes injected fuel droplets with the air mass. • Assists combustion of fuel droplets. • Peels off the combustion products from the surface of the burning drops as they are being consumed. • Supplies fresh air to the interior portion of the fuel drops and thereby ensures complete combustion. • Reduces delay period. • Reduces after burning of the fuel. • Better utilization of air contained in the cylinder.
- 51. TYPES OF AIR MOTION The air motion in a diesel engine is generally caused by either by the intake port during the suction stroke or by combustion chamber geometry during the compression stroke. Three different elements of the air motion present during intake to expansion strokes in a diesel engine cylinder have been classified as 1) Swirl 2) Squish 3) Turbulence
- 52. Swirl Motion Swirl is defined as the organized rotation of the charge about the cylinder axis. It is created by bringing the intake flow into the cylinder with an initial angular momentum. Swirl is generated during the intake process in DI diesel engines by the intake port and subsequently by combustion chamber geometry during the compression stroke.
- 53. Squish Motion The squish motion of air is brought about by a recess in the piston crown. At the end of the compression stroke, the piston is brought to within a very small distance from the cylinder head. This fact causes a flow of air from the periphery of the cylinder to its center and into the recess in the piston crown.