1. Compression Ignition Engines
Shaping the Future
Compression Ignition Engines

2. ~ a representation of the Compression Ignition/Diesel Engine
Compression Ignition Engines
Constant Volume plus Pressure Combustion
The Dual Cycle
~ a representation of the Compression Ignition/Diesel Engine
Rudolf Diesel

3. Compression Ignition Engines
Diesel Engines

4. Large Ship Diesel Engines
Compression Ignition Engines
Large Ship Diesel Engines

5. Compression Ignition Engines
CI Engine Characteristics:
High pressure fuel injection
In-cylinder air-fuel mixing
Auto-ignition
High “Energy” Density – BMEP
(Torque/Litre)
Speed limited (mixing time limited)
High low speed Torque
High Particulate (Smoke) Exhaust Emissions
High Peak Cylinder Pressures

6. Spark Ignition ‘v’ Compression Ignition
Petrol (Gasoline)
Diesel Oil
Spark ignition of Air and Fuel mixture
Compression ignition of Air & Fuel mixture
Typical Compression Ratio 8: 1 to 12:1
Typical Compression Ratio 12: 1 to 24:1
Fuel mixed with Air prior entering the cylinder
Fuel mixed with Air while in the cylinder
Normal Air – Fuel mixture ratio: 14.7 : 1
Air – Fuel mixture ratio; 20:1 to 70:1
Load Control - quantity of Air-Fuel mixture (using a throttle)
Load Control – “strength” of Air-Fuel mixture (amount of fuel)
Engine speed range 500 to 7000 rpm
Engine speed range 500 to 5000 rpm
Maximum torque at mid speed range
Maximum torque at lower speed range

7. In-Cylinder Air Flow Management
Re-entrant Toroid
MAN wall wetting system
Direct Injection
Most Common
Indirect Injection
Pre Chamber
Swirl Chamber
Not generally used in modern passenger car applications

8. Re-Entrant Toroid Combustion Chamber
Vertical injector for symmetric fuel distribution
High swirl (helical) inlet port –
Swirl ratio approx 3 + (air swirl speed/engine speed)
Reduces high engine speed volumetric efficiency
Increases thermal losses (due to high charge motion)
Minimum “bumping” clearance for high compression ratio – can lead to valve angle/overlap problems
bumping clearance = height between top of piston and cylinder head at TDC

9. Re-Entrant Toroid Combustion Chamber
Piston Details;
Reinforced Top Ring Groove
Gallery Cooled Piston Undercrown

10. Injection Technology
Recent advances in injection technology have had significant impact on the development of combustion systems and have blurred the distinction between gasoline & diesel combustion systems
Highly flexible pressure direct injection systems coupled with good air management have enabled the development of new combustion systems, e.g.
Gasoline Direct Injection
Homogeneous Charge Compression Ignition
What are the injection systems and how do they affect fuel preparation and the subsequent combustion ?

11. Injection Systems Traditional 2 Stage Injector
Opens as a consequence of an increase in fuel pressure provided by a single pump that feeds all injectors/cylinders
Initial (low pressure) lifts against primary spring to provide an almost type of pilot injection
Increased pressure causes the secondary system to open and deliver the main injection
Rapid closure of the injector after fuel delivery is important to prevent any ‘dribble’ effects that create Hydrocarbons exhaust emissions (HC)

12. Injection Systems Pump Unit Injector
Produces pressure only when required (up to 2000bar)
Uses a controlled jitter for pre-injections
Will disappear with introduction of EURO5, because post-injections to burn down particle filters are not possible

13. Injection Systems
Solenoid Actuated Injectors provide good multi – injection control capability
Closed
Open

14. Injection Systems
Solenoid Actuated Injectors provide good multi – injection control capability
Closed
Open

15. Injection Systems
Piezo Actuated Injectors also provide good multi – injection control capability

16. Multiple Injection (1) – Pilot – combustion initiation
(2) – Main – diffusion combustion
(3) – Post – HC clean up , catalyst warm up

17. Common Rail Injection Systems
Fuel Reservoir (Common Rail)
High Pressure Pump
Solenoid or Piezo Actuated Injectors

18. Common Rail Injection Systems
Common Rail High Pressure Fuel Pump

19. Injection System Pressures
This suggests that injection pressure is the main (only) parameter that affects output
~ It is really all about fuel spray optimisation, mixing and control !

20. Fuel Spray Optimisation
Important Parameters :
Overall spray structure
Fuel Atomisation
Fuel Spray Penetration
Droplet Evaporation
Air – Fuel Mixing
Nozzle Design is Key

21. Injector Nozzle Design
Spray Characteristics;
High initial velocities , reduced by drag
Droplet formation during break up – typical diameters 25 to 10 micron
Spray tip penetration dependent on injection pressure, charge density, swirl ratio etc
Droplet evaporation rates are dependent on droplet size, local temperatures and air entrainment rates

22. Injector Nozzle Design
Conical Spray
Multi – Hole
Fuel “Sac”

23. Multi-Hole Fuel Spray Patterns

24. Fuel Spray Optimisation
Effect of Injection Pressure on Droplet Size ….
Influence of nozzle hole length
- the shorter the better?
Influence of nozzle hole diameter
– the smaller the better?

25. Fuel Spray Optimisation

26. Fuel Spray Optimisation
Pressure and temperature control spray pattern, hence droplet size
Constant:
injection pressure
Variable:
environment pressure and environment temperature
Constant:
environment temperature Variable:
injection pressure and environment pressure

27. Fuel Spray Optimisation
Droplet Evaporation
Droplet evaporation rate initially increases due to its temperature rise – it then slows as its velocity reduces and temperature stabilises
Within approx 1 msec 90% of the evaporation is complete
Within warm engines air entrainment is the limiting factor, within cold engines droplet evaporation may be the primary limiting cause

28. Thank You for Listening