08-10-2012, 05:00 PM
THE AUTOMOTIVE DIESEL ENGINE
THE AUTOMOTIVE DIESEL.ppt (Size: 1.53 MB / Downloads: 50)
Diesel Combustion
Fuel sprayed in cylinder near TDC
Atomization, vaporization & mixing delay ignition
Ignition occurs wherever conditions right
Combustion rate controlled by injection characteristics (injection rate, spray angle, injection pressure, nozzle size and shape), chamber shape, mixture motion, & turbulence
Glow plug may be used to aid cold starting
Power output controlled only by amount of fuel injected
Fuel Injection Systems
Electronic distributor pump
Electronic unit injector (EUI)
High-pressure common rail
Boosting
Most diesels boosted (i.e., turbocharged)
Boosting helps power & torque
Boosting helps fuel consumption
Boosting facilitates torque curve shaping
Boosting helps relative package size
Boosting increases cost but is good value
Boosting Systems
Current Technologies
Waste-gate turbocharger
Variable nozzle turbine turbocharger
Future Technologies
Two-stage turbocharging systems
Electric motor driven compressor, turbine, or both
Dual range compressors with one turbine
Exhaust Emission Control
HC (challenging)
Nozzle design
Catalyst (HC & exhaust odor)
CO (less challenging)
NOx (most challenging)
Injection timing
EGR
Injection rate shaping
Lean NOx catalyst
Combustion chamber shape optimization
Summary Diesel Engines
Advantages:
Efficiency (most efficient prime mover)
Emissions (low CO, CO2, good durability)
Very high torque and performance
Disadvantages:
Emissions (more challenging to control NOx, particulates)
Higher cost
Heavier
Noise (more challenging to make quiet)
Future Trends
Factors
Global warming (favors diesel)
Energy resources (favors diesel)
Government policy (low fuel tax unfavorable for diesel)
USA
Truck use increasing
Car use discouraged by low fuel tax
Higher recent fuel prices and higher CAFE threat driving some introduction
Europe
New technology (4-valve DI, common-rail injection, particulate traps)
Diesel car sales up dramatically (currently 50% of new car market)
Being marketed as performance engine