Diesel Engines Mechanical SSSP | Fuel Systems SSSP | HP-Fuel Systems SSSP | Injection Timing Flashcards
What are 2 major functions that determine variables factored in to efficiently control injection timing?
1) Fuel Burn Rate & 2) Time available for Combustion
Identify 8 variables that affect combustion events & thus HPI timing.
1) Fuel Temp
2) Intake Air Temp
3) Coolant Temp
4) Oil Temp
5) Boost Pressure
6) EGR Rates
7) Engine Load
8) Engine Speed
In most diesel engines, peak cylinder pressure should occur approximately when?
10-15° of crankshaft rotation after top dead cylinder (TDC).
Identity the 2 most critical factors influencing Fuel Burn Rate.
Cylinder Pressure & Temperature
Optimally, with engine under load, should HPI timing advance or retard? Why?
Retard. More diesel has to be injected to supply more power to match greater energy demands; more fuel injected = higher cylinder pressure = higher fuel burn rate = earlier combustion than intended (e.g., failure to maintain consistent speed and smooth operation of engine), if not compensated for.
What is the NATURAL relationship between engine speed & injection + combustion events.
As the engine speed increases, injection + combustion events do NOT speed up proportionally; while the crankshaft can and may be turning through more degrees of rotation per second or unit of time, injection + combustion (e.g., burn-time, basically an independent static value not a dynamic dependent variable) events nonetheless eventually cannot be completed as quickly because they require a (theoretically and currently physically, longer) fixed amount of time.
Given a burn time of…
Cold Weather Conditions: Distinguish injection timing during cold starts (engine cranking) vs engine running.
When running, timing is advanced. Only when cranking, timing is retarded. (see “Injection Timing and Cold Starting” section on page 483, under Injection Timing section of CH 16)
What are 7 Engine Parameters that are decreased when Engine Timing is advanced?
1) PM @ Rated Speed
2) PM @ Low Speed & Load
3) HCs
4) Fuel Consumption (BSFC - Brake-Specific Fuel Consumption - the rate of fuel consumption of the engine divided by the power produced by the engine)
5) Intake Manifold Boost Pressure
6) Exhaust Temperature
7) Coolant Temperature (heat rejection)
What are 4 Engine Parameters that are decreased when Engine Timing is retarded?
1) Cylinder Pressure
2) Oxides of Nitrogen (NOx)
3) PM @ Peak Torque
4) Combustion Noise
What are 4 Engine Parameters that are increased when Engine Timing is advanced?
1) Cylinder Pressure
2) Oxides of Nitrogen (NOx)
3) PM @ Peak Torque
4) Combustion Noise
What are 7 Engine Parameters that are increased when Engine Timing is retarded?
1) PM @ Rated Speed
2) PM @ Low Speed & Load
3) HCs
4) Fuel Consumption (BSFC - Brake-Specific Fuel Consumption - the rate of fuel consumption of the engine divided by the power produced by the engine)
5) Intake Manifold Boost Pressure
6) Exhaust Temperature
7) Coolant Temperature (heat rejection)
Describe the effect on engine starting between advancing or retarding injection timing.
Retarded contributes to easier starting, Advanced contributes to harder starting.
Describe a way that engine manufacturers work to simultaneously minimize NOx + PM production.
ENG OEMs aim for finer atomization of fuel that also shortens ignition delay time.
on mechanical systems injection, timing needs to be set within what margin of OEM SPEC for correct emission control? For electronically controlled (electronic systems injection) engines?
Mechanical - within 1/2 (.5) degree of the OEM’s specifications.
Electronic - injection timing variations are controlled to less than 1/10th (.1) degree of precision.
