In Europe, seven out of ten luxury cars are diesel powered, new diesel passenger car sales are reportedly near 40 percent, and still trending upward.
One of the main reasons for this rise in diesel popularity is the emergence of Electronic Diesel Control (EDC). EDC has enabled cleaner, more complete combustion with lower emissions, greater economy and power, and lower noise not previously achievable with either direct or indirect (pre-cup) combustion chambers. According to the Diesel Technology Forum, new diesel engine PM (Particulate Matter) emissions have been reduced 83 percent and NOx emissions by 63 percent since 1988. Moreover, HC, CO and C02 emissions, already inherently low with diesel engines, have improved.
“Clean diesels” have the ability to more completely and efficiently burn fuel within the engine. The primary enhancements include improved fuel delivery systems, improved configuration of combustion chambers, and turbocharging.
Fuel delivery systems
Fuel delivery systems have gone largely from RPM and load dependent mechanical governing systems to electronic diesel control, or EDC. The fuel injection industry is moving away from mechanically governed in-line and distributor-type injection pumps to common rail systems (CRS), hydraulic electronically controlled unit injectors (HEUI) and other alternatives.
Fuel injection is now done under much higher pressures for complete atomization of fuel sprayed directly into the superheated air of the combustion chamber. Furthermore, electronic control means varying rates of fuel delivery per cylinder and crankshaft degree can be done under varying speed and load conditions for quieter and smoother performance.
To reduce ignition clatter at idle, a smaller “pilot” spray initiates the combustion cycle, with greater amounts of fuel following ignition. Delivery tapers off near the completion of the combustion cycle for complete burn and low emissions.
Combustion chamber configuration
The shape and depth of the combustion chamber and piston, the number and placement of valves, intake ports designed for greater swirl, and placement of the injectors, all play a role in clean-diesel design and reduction of Particulate Matter and NOx.
Turbocharging (for improved swirl and greater air volume) and air intake intercoolers (to cool down the compressed intake air) increase volumetric efficiency and reduce NOx. Turbos also mean more power can be derived from smaller displacement (less weight) engines for greater fuel economy. Aftermarket accessories and electronic “chips” are increasingly popular for improving performance within clean air limits for the popular clean-technology diesel engines. OBD-II is now standard.
Thanks to electronics and the inevitable incorporation of 42 volt systems, other improvements include “instant-hot” glow plugs; variable valve timing, EGR cooling; electronic variable geometry/electronically assisted turbocharger nozzle and waste gate management; electric water pumps, PS pumps, and A/C compressors; drive-by-wire, brake-by-wire; collision avoidance; increased OBD (monitoring the entire powertrain); satellite connectivity; and more. Other refinements also include various types of exhaust after-treatment (catalysts) for NOx, and particulate traps for reduction of PM.
On-board technology can’t produce all the necessary improvements alone. The much lower sulfur content in diesel fuel will help, as well as dual-fuel diesels that make use of direct-replacement high-pressure injectors or use electronically controlled port-type gaseous injectors.