Compression Ignition Engines Shaping the Future Compression Ignition Engines

~ 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

Compression Ignition Engines Diesel Engines

Large Ship Diesel Engines Compression Ignition Engines Large Ship Diesel Engines

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

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

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

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

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

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 ?

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)

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

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

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

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

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

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

Common Rail Injection Systems Common Rail High Pressure Fuel Pump

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 !

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

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

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

Multi-Hole Fuel Spray Patterns

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?

Fuel Spray Optimisation

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

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

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