Focus on Training Section: Unit 2

Transcription

1 All Pump Types Page 1 1. Title Page Learning objectives Become familiar with the 4 stroke cycle Become familiar with diesel combustion process To understand how timing affects emissions To understand the relationship of engine speed to injection lag 2. Peak Torque Be able to describe Torque and Power Torque is what gets you up the hill Power determines how fast you get up the hill Point where the greatest amount of torque is developed 3. Rated Speed Torque Be able to describe Rated Speed Torque Torque that is produced at the highest horsepower that can be safely extracted from the engine continuously Rated Speed Torque is lower than Peak Torque

2 All Pump Types Page 2 4. Torque Drop Understand Torque Drop Difference between Peak and Rated Speed Torque Briefly mention how the use of a pump torque screw will lower the Rated Speed Torque thus causing a greater torque drop Full load conditions cause the engine to slow to the Peak Torque RPM Spark ignition engines tend to have a greater Torque Drop than diesels 5. Gasoline Cylinder Construction Be able to point out main components Lower compression Lighter component design Throttled air intake Spark ignition 6. 4 Stroke Cycle Gasoline Intake Inlet valve open Draws air and fuel into cylinder Compression Both valves closed Fuel air mixture compressed due to piston moving towards head

3 All Pump Types Page Stroke Cycle Gasoline Power Spark plug ignites fuel / air mixture Gas expansion drives piston down creating power Exhaust Momentum moves piston up Exhaust valve opens allowing exhaust gases to be evacuated from cylinder 8. Diesel Cylinder Construction Be able to point out main components High compression Stronger (heavier) component design Non-throttled air intake Ignition due to temperature rise from compression 9. 4 Stroke Cycle Diesel Intake Inlet valve ope Draws air into the cylinder Compression Both valves closed Air compressed due to piston moving towards head Fuel injected near the end of the compression stroke, depending on timing

4 All Pump Types Page Stroke Cycle Diesel Power Both valves closed Heat of compression ignites fuel / air mixture Fuel continues to be injected and burned Expansion of gases drives piston down creating power Exhaust Momentum moves piston up Exhaust valve opens allowing exhaust gases to be evacuated from cylinder 11. Indirect vs. Direct Injection Direct Injection Advantages Higher fuel economy Easier starting Reduced heat loss Lower compression ratio Manufacturing benefits Disadvantages Rough running Noisier Worse emissions Higher combustion pressure Higher injection pressure Higher loads on pump and drive Requires multi hole nozzle Indirect Injection Advantages Quieter operation Lower injection pressure Lower loads on pump and drive Better emissions Single orifice nozzle

5 All Pump Types Page Indirect vs. Direct Injection (cont.) Disadvantages Higher compression ratio Harder starting Increased heat loss Worse light load performance 12. Four Stages of Combustion Graph Vertical = pressure or temperature Horizontal = crank angle Bell curve in red is crank position from start of compression to end of power stroke Yellow curve is pressure or temperature in the combustion chamber SOI - Start of injection into combustion chamber SOC - Start of combustion. Heat of compression increases air temperature to the temperature required for auto ignition of the fuel EOI - End of injection, nozzle closes Four Stages 1. Ignition Delay - Starts at SOI, ends at SOC. Fuel is not ignited 2. Uncontrolled Burn - Rapid increase in pressure and temperature. Fuel injection during ignition delay and what is continuing to be injected burns. This is what causes the audible diesel knock

6 All Pump Types Page Four Stages of Combustion (cont.) 3. Controlled Burn - Fuel is burned at the rate it is being injected at. Creates power 4. After Burn - Injection ceases, residual fuel in chamber continues to burn 13. Timing & Emissions Timing that is too advanced causes a long ignition delay (large quantity of fuel injected before auto ignition). This fuel when burned during the uncontrolled burn stage causes extreme heat to build in the combustion chamber. The oxygen in the air in the combustion chamber due to this high temperature combines with nitrogen to form colorless emission gases called Nitrous Oxides Timing that is too retarded causes a short ignition delay (small quantity of fuel injected before auto ignition). Temperatures created during the uncontrolled burn stage is comparatively low causing incomplete combustion of the fuel which is exhausted as particulate matter (PM) which is another form of emission. Black Smoke

7 All Pump Types Page Timing & NOX / PM Emissions Graph shows by advancing the timing NOX gases increase and by retarding the timing PM emissions increase. Ideal timing is where both emission curves cross. 15. Injection Lag The time that can be expressed in engine degrees for the pressure wave origination at the pump to travel through the line to the injector. Time between start of pumping, SOP, and start of injection, SOI. 16. Injection Lag Even though the speed of the wave remains at 1500 meters / second, as engine speed increases, injection lag in degrees increases.

8 All Pump Types Page Injection Lag at Idle There is 2.6 degrees between SOP and SOI at 800 ERPM 18. Injection Lag at Rated Speed At 2400 ERPM Injection Lag has increased to 7.6 degrees. To fix the SOI at the same point thus not increasing the ignition delay the pump timing (SOP) must be advanced (speed advance) 19. Light Load Advance Under full load condition, the metering valve is fully open allowing a full charge of fuel into the pumping chamber behind the plungers. This means that the point where the rollers contact the cam is the same point as the SOP

9 All Pump Types Page Light Load Advance Under light load conditions the metering valve is partially closed, only allowing a partial charge of fuel to enter the pumping chamber behind the plungers. Because plungers only travel out as far as the charge of fuel pushes them, yet the shoes / rollers travel all the way out, there is a space between the plungers and the shoes / rollers. Because of this, the rollers contact the cam and have to travel up the cam ramp to close this gap and thus the SOP begins after the gap is closed. Light load advance compensates for this to allow the point of roller contact and the SOP happen at the same time. This is not necessary for DS and DE pumps as they take a full charge of fuel for every charging event. Notes 21. Cold Start When fine fuel droplets come in contact with the relatively cool components of the combustion chamber during cold start operation they puddle into slower burning larger drops. Some of this fuel is not burned in the engine but instead released into the atmosphere as white smoke. Increasing the advance thus increasing the ignition delay at starting, will cause a high temperature during the uncontrolled combustion stage. This increase of temperature will quickly raise the component temperatures, preventing extended periods of white smoke production