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Diesel particulate filters were developed as one of several emissions reduction strategies for Tier 4 Interim and Tier 4 Final engines a few years ago. But where and when they can, manufacturers such as Doosan are designing their smaller engines so that a DPF is not needed. Why?
“It requires high-cost maintenance, such as ash cleaning, a large space for mounting, potentially negative fuel economy, risk of thermal damage, frequent service claims and a complex design,” says Kwangsup Hwang, Doosan Engine Group.
In order to avoid those issues Doosan developed a line of DPF-free compact engines with three models:
To make an engine clean enough to forego the DPF, Doosan engineered a new combustion system it calls Ultra Low Particulate Matter Combustion, or ULPC. It optimizes the design of the piston bowl, fuel injectors, cylinder head and other components to use the oxygen as much as possible in the combustion chamber, says Hwang.
The new engines have fixed valve timing, a maximum of five injections per cycle with 26,000-psi injectors, and an optimized single turbocharger. EGR rates were increased in some engine operating points (rpms and torque loads) and reduced in others to optimize engine performance, fuel economy and emissions reduction.
A maintenance-free diesel oxidation catalyst (DOC) was developed for high efficiency removal of the soluble organic fraction of the particulate matter (PM) throughout the engine’s lifetime. Any catalyst will deteriorate from exposure to exhaust, Hwang says, so it was important to design the engine to minimize DOC deterioration while maintaining high levels of PM removal.
The D34 also uses SCR as part of its emissions reduction package.
Hwang adds that a large portion of any engine’s particulate matter is unburned oil. To counter this in the new engines, Doosan redesigned the piston shape and piston ring pack to minimize oil consumption.
Bobcat, a sister company to the Doosan Engine Group, says the new engines will be added to some of its Tier 4 machines for 2014.