1. OHIO TECHNICAL COLLEGE June 27th, 2018 Cleveland, OH
Sean Bennett
Cengage Learning

2. Diesel Combustion and Emissions
A primer in cylinder combustion dynamics and how end gases are produced modern diesel engines

3. Fundamentals of in-cylinder combustion – keeping it simple
What is air?
What is fuel?
Physics of engine torque production
Chemistry of combustion
End gas combustion

4. Diesel Cycle Review

5. Intake Turboboosted air forced into cylinder
Excess air: depends on mode of operation – varies between as much as 600% at idle to as little as just over stoichiometric at peak torque (λ< 1)
Air is a mixture of N2 (78%) and O2 (21%)
EGR is also introduced into the cylinder
EGR cut percentage varies by manufacturer and mode of operation

6. EGR
Exhaust discharge is the most convenient source of ‘dead’ (unreactive) gas
It dilutes the intake charge (of oxygen) and lowers combustion temperatures
It can be cooled and may be ‘cleaned’ (Cat CGI) sourced downstream DPF
EGR cut-percentage is ECM controlled

7. Compression and Power Strokes

8. Lean Burn Technology
Emissions tightrope: combustions temperatures must be managed
High temps (lean burn): ++ NOx
Low temps: ++ HC (incl PM)
1988 to 1997: ECM managed
After 1997: phased intro of emissions hardware

9. ASTM ULS Diesel Fuel Petrochemical HC: + 85%C + 14% H
Max Sulfur: 15 ppm (0.0015%)
CN rating: defines ignition temp
#2D: (min CN 40) summer cut + 45
Ignition temp CN 40: F (2900 C)

10. High injection pressure driven through a fixed orifice = smaller fuel droplets

11. Diesel Fuel Injection Pressure
Diesel fuel is pumped through a fixed flow area defined by the injector orifice size
Pressure at the injector orifice(s) (rail pressure) determines fuel droplet size
Optimum droplet size: 10 – 15µ (microns)

12. Crank Leverage Geometry

13. Hydromechanical era: hard values – combustion events dependant on pump port closure

14. HD Diesel CR System Layout

15. Electrohydraulic Injector (EHI)

16. Paccar Delphi CR System

17. CR Injection Control and Combustion

18. Multipulse Diesel Fuel Injection
Controls injection rate to manage cylinder pressures during power stroke
Managing cylinder pressure = smooth mechanical transition of torque to the engine powertrain (crankshaft)
Optimizes combustion of fuel to minimize end gas pollutants

19. Diesel Exhaust Process
End gases must be removed from cylinder
Begins when exhaust valves open: occurs before BDC on the power stroke

20. Exhaust Purge Events
Pressure differential: gas blowdown during piston downstroke
Inertial purge: piston at BTDC
Displacement: piston moves to TDC
Scavenging: Exhaust valves closing, intake valves opening. Maybe extended in diesel engines.

21. Valve Operation

22. End gas composition CO2 (a pollutant since 2007 Supreme Court ruling)
H20 (a GHG when produced in a redox reaction)
Other:
NOx PM
Uncombusted gaseous HC
Uncombusted liquid HC

23. DOC Diesel oxidation catalyst Uses platinum and palladium catalysts
Used for a generation in diesel engines and is located upstream from DPF
Reaction temps range from C

24. DPF A soot trap for emission solids known as particulate matter (PM)
PM is entrapped by filters and collected
When soot reaches a threshold value, the DPF must be regenerated
Regen reduces soot to unreactive ash

25. DPF Entrapment Principle

26. DPF regeneration modes
Passive: set to occur when soot build-up has reached a threshold and engine exhaust temps are high enough
Engine is usually under load and the vehicle is running at highway speeds
Exhaust gas heat (600 C plus) is used to burn-off soot to unreactive ash
Ash is then collected

27. DPF regeneration modes
Active: occurs when DPF soot levels exceed a threshold value
ECM-controlled when vehicle operating conditions permit
ECM-diagnostic software generated
May require: fuel to be injected into the exhaust gas and spark-assist ignition

28. SCR
NOx reduction agent used in gasoline fueled engines (rhodium) only functions as a catalyst when stoichiometry is <15:1
SCR uses ECM-managed DEF (aqueous urea) injection to reduce NOx compounds back to elemental O2 and N2
DEF is a consumable that must be replenished: levels are ECM-monitored and are EPA-required to progressively cripple the engine if refill alerts are ignored

29. Sean Bennett Cengage Learning
Discussion
Thanks
Sean Bennett Cengage Learning