In most respects, the challenges for diesel engines are quite different than either spark ignition (SI) engines or the electrical/electronic portion of hybrids. While the first diesel engine-powered production car, the Mercedes-Benz 260D, was introduced more than 70 years ago, it took modern electrical and electronic components to overcome some of the major problems. Electronics continues to provide solutions to challenges such as improved performance, reduced emissions including soot (particulates) and nitrogen emissions (NOx) and in stark contrast to the hybrid, supplemental heat. Todayís diesel engines use very high-pressure direct injection (over 1000 bar) and techniques such as lean NOx trap (LNT) and injecting urea in exhaust after-treatment to reduce NOx.
HIGH-PRESSURE PIEZOELECTRIC INJECTORS
Direct injection has been used on diesel engines for more than a decade and is now being used in advanced internal combustion engines to achieve higher efficiency and reduce emissions. In addition to solenoid-driven units, piezoelectronic injectors pioneered by Siemens VDO, now part of Continental, have been available on diesel engines since 2000. With piezo injection, electricity applied to pressure-sensitive crystalline discs changes their structure producing a geometric change sufficient to activate the hydraulic opening of the injector needle. Compared to the solenoid actuated injectors, piezo injectors are up to four times faster and operate at higher pressures (over 2000 bar) to optimize injection before, during and after the combustion process. In 2008, the companyís piezo common rail (PCR) system is used on Fordís 6.4-l PowerStroke diesel engine in the F-Series Super Duty pickup truck.
One of the approaches to reduce NOx emissions on diesel engines uses a Selective Catalytic Reduction (SCR) system. Injecting ammonia-rich urea in a SCR system reduces nitrogen by up to 80 percent. Ammonia emissions are a potential problem, but with an ammonia sensor developed by Delphi, engineers can directly measure tailpipe ammonia in a closed-loop control system. Taking advantage of expertise from designing and manufacturing oxygen sensors, Delphi Research Labs. developed an ammonia-sensitive material that is deposited onto a thick film ceramic substrate similar to the type used in oxygen sensors. By detecting excess ammonia in the exhaust gas within a range of 0 to 100 ppm, the sensor allows continuous optimization of the urea dose.
PTC AUXILIARY HEATER
In contrast to hybrid vehicles that require special cooling for the electronics, modern diesel engines do not generate sufficient heat to warm the passenger compartment in cold climates, especially under stop-and-go conditions. Some estimates place the use of auxiliary heaters at more than 65 percent for European diesel-equipped vehicles. BERUís positive temperature coefficient (PTC) heater provides rapid heating requiring only 10 sec preheating at -20C. In Fordís Super Duty F-250 with the 6.4-l diesel engine, a 1,300W unit delivers the additional heating capacity. The PTC auxiliary heaters are available in relay, electronic relay, analog electronics and digitally controlled versions. In the digital version, a microcontroller regulates the heating element and connects into the vehicleís bus through CAN or a LIN network.