Big emissions technology in small package: two models in new Yanmar L series line incorporate rudimentary EGR for Tier 2 - diesel engines

While most of the heat and light being generated by tightening emissions regulations has been in heavy-duty on-highway trucks and larger off-highway and industrial markets, virtually all engines large and small face their own emissions challenges.

For small diesel engines under 10.8 hp (8 kW), that next hurdle is Tier 2, arriving Jan. 1, 2005, when the emissions restrictions Fall to 5.8 g/bhp-hr CO, 5.5 g/bhp-hr NMHC and N[O.sub.x] and 0.58 g/bhp-hr PM.

To meet these new challenges, Yanmar has developed a new generation in its L series line of single-cylinder engines designed to meet the new emissions standards while maintaining the same reliability, and dimensional parameters as the existing L series line.

The new engines are the L48V, rated 4.5 hp; the L70V, rated 6.7 hp; and the L100V, rated 9.3 hp. Rated speed for each of the engines is 3600 rpm. They are targeted toward a range of small horsepower applications, including pressure washers, power generation and military. Complete specifications are in the accompanying table.

Most interestingly, one of the key strategies allowing the two largest new engines to meet the Tier 2 standards is a technology most often associated with much bigger engines--exhaust gas recirculation (EGR).

"I've not heard of anybody else using it on this size engine," noted Jeff Williams, manager, sales & marketing for Yanmar America Corp., Buffalo Grove, Ill. "It is very simple science, but it does the job."

Yanmar's EGR system is indeed simple, yet effectively provides for the recirculation of exhaust gas into the cylinder, a method used in one form or another, on nearly all large heavy-duty truck engines. The basic principle behind EGP, is directing a portion of exhaust gas back into the cylinder to better regulate temperature within the cylinder. Temperature control is critical, as it enables the formation of some exhaust gas components, particularly N[O.sub.X] and HC, while encouraging more complete combustion, which reduces the formation of PM.

Yanmar's system consists primarily of a small drilled passage that connects the exhaust port to the intake port of the two-valve engine. During the exhaust stroke, a small portion of exhaust gas is routed through this passage back into the cylinder, where it is mixed with intake air.

The introduction of hot exhaust gas serves to keep the combustion air warmer under low load conditions, reducing the formation of CO and HC. Along with that, engine timing is retarded slightly, reducing N[O.sub.X] formation, the company said.

Yanmar has made other changes to the engines designed to improve emissions performance. The pump/line/ nozzle direct-injection system has been optimized to increase injection pressure. The pump plunger diameter has been increased and roller type tappets are now being used.

The cylinder block has been redesigned to accommodate a longer (3 mm) piston stroke than the previous generation engines. The crankshaft, connecting rod and balancer shaft are also new.

For all of those changes, Yanmar has managed to keep the crankcase dimensions the same, along with the same center positions for the crankshaft, camshaft and balancer. The position of the fuel tank, air cleaner and muffler are unchanged. Finally, the general dimensions--length, width and height--remain unchanged from the previous generation.

"Obviously, what we're trying to do is limit the impact on our current customers," Williams said. "If you look at the history of these engines, from the pre-EPA LA engines, to the current LE engines, to tiffs new series, we have not changed the mounting geometry at all. The mounting feet and the bolt patterns have been the same all the way through and that's been deliberate.

"We don't want our existing customers to have to make changes to use these engines. Engineering costs are critical these days and that's one thing that will help us sell these engines."