Equipment World Digital Magazine
Issue link: http://read.dmtmag.com/i/748269
EquipmentWorld.com | November 2016 27 S ince the fi rst emissions regulations for on-highway diesels arrived in 1974, four primary components of emissions have become well controlled: carbon monoxide (CO), oxides of nitrogen (NOx), hydrocarbons (HC) and particu- late matter (PM). Now the federal government has its sights on regulating greenhouse gases and improv- ing fuel economy (see side- bar on page 24). This has led truck OEMs to re-examine their designs in order to meet these standards, while also meeting customer demands. Advances in drivetrain technol- ogy are yielding higher power density (power output for a given size of engine), allowing the use of smaller-displacement, lighter- weight engines for improved fuel effi ciency with no loss of performance. Other changes further improve fuel economy; the net improvement is typically in high single-digit percentages, but may be more. Here's a summary by drivetrain component: Engines The bowl-shaped depression on the top of a piston is there to improve combustion effi ciency, thereby improving fuel effi ciency and reducing PM. Manufactur- ers have been working on bowl shapes for years and have found gains once again. So-called "wave" pistons have protrusions into the bowl from the sides to increase compression and further enhance fuel/air mixing for more complete combustion. Decades of improvements to unit injectors have made them effi cient, but manufacturers are now switching over to common rail injection. Where a unit injec- tor creates fuel pressure on each intake cycle, common rail injec- tion holds high pressure in the system at all times. The injector merely controls the delivery of that pressurized fuel. Common rail injection allows higher pressures, which improve fuel atomization and distribu- tion and therefore combustion effi ciency. Typical pressures for common rail are 25,000 to 35,000 pounds per square inch, or about twice that of most unit injectors. Some common rail systems de- liver up to 50,000 psi. (Fuel pres- sure is often expressed in bars; 1 The Volvo D13 with turbo compounding provides an additional 50 horsepower and an improvement of up to 6.5 percent in fuel effi ciency. Both it and the standard, non-turbo- compounding D13 feature wave piston design and hybrid common rail fuel injection.