Physics and chemistry dictate that most Tier 4 Interim engines follow a common design formula to reduce emissions. Above 75 horsepower most manufacturers have increased fuel injection pressures, boosted turbos, ramped up exhaust gas recirculation (EGR) rates and added aftertreatment that traps or burns off what the Environmental Protection Agency doesn’t want going out the exhaust stack.
Komatsu follows this basic formula too, but it has leveraged its expertise in hydraulics to perform some of these functions in a unique way, specifically the control of its variable geometry turbos (VGTs) and EGR valves.
On a VGT, the vanes of the turbo open and close to increase or decrease the air being fed into the engine. Other ways to do this are to use twin turbos, two-stage turbos, or waste gates that bleed off excess air.
Komatsu has opted for the VGT style turbo above 74 horsepower (see chart on page 42). But unlike most designs in which the vanes are controlled electro-mechanically, Komatsu uses hydraulic pressure. “We feel the hydraulic actuation is more advantageous because the hydraulics provide more power, and it’s more precise,” says Doug Morris, director product marketing, Komatsu America. “It optimizes the airflow of the whole engine.”
Precise control of the turbo is not only important in maintaining engine power, but in Tier 4 Interim engines this air flow is critical to the effective functioning of the exhaust aftertreatment, Morris says. Komatsu’s VGT adjusts to assist with active regeneration, but it also reduces soot at the point of creation in the cylinder, reducing what passes downstream into the DPF.
Komatsu increased the amount of exhaust gas recirculating back into the engine, as have most manufacturers transitioning from Tier 3 to Tier 4 Interim. The purpose of pumping exhaust gas back into the cylinders is to dampen combustion temperatures and thus reduce the amount of nitrogen oxides or NOx flowing out the exhaust valves (NOx is one of the emissions the EPA regulates.)
