Search Results

Diesel engine NOx emissions requirements have become increasingly stringent over the past two decades. Engine manufacturers have shown through the use of EGR and SCR technology that these requirements can be met. However, the desires for improved fuel efficiency, lower overall cost, and potential legislation to reduce NOx levels further increase the demand for higher DEF dosing rates. To meet this demand, a new DEF mixing technology has been developed. This paper describes the development methods used to create a compact, in-pipe mixer which utilizes an optimized wire mesh along with swirling flow to permit high DEF dosing rates without deposit formation. Its excellent mixing characteristics allowed for high NOx reduction to be achieved. Utilization of this technology makes it possible to reduce regeneration frequency, reduce the overall size of the SCR system, possibly eliminate the EGR system, and improve fuel efficiency through combustion enhancements.

This paper describes the evolution in diesel engine SCR technology used on tractors ≻130 kW. Details on the SCR technology evolution from Tier 3 to Tier 4 interim are disclosed. Furthermore, this paper demonstrates how state-of-the-art SCR technology can make a non-EGR diesel engine meet Tier 4 final emission limits without using particulate filtration. Initially, it was assumed that Tier 4 aftertreatment systems would use aftertreatment for NOx and PM, combined with an advanced combustion concept and EGR. However, with this solution, one can expect disadvantages such as: cost, complexity, high heat rejection, large space claim and less than optimal fuel efficiency. Furthermore, active PM filter regeneration is challenging and can be hazardous in certain agricultural applications. A Tier 4 final engine without PM filtration would require a SCR aftertreatment system with NOx conversion efficiencies in the range of 90-97% on all relevant conditions for the entire life of the engine.

This paper describes the optimization process of a small single-cylinder research HSDI diesel engine, starting from a conventional combustion towards split-injection low-temperature combustion. Targets for emissions, fuel consumption and combustion noise are defined with the characteristics of low temperature combustion in mind, in other words, high CO, HC and combustion noise but low soot and NOX. In this investigation the targets are defined for a medium-load working modes of a typical small four-cylinder turbo-charged diesel engine, equipped with a particulate trap and oxidation catalyst. They are introduced into an objective target function which is a guide for the optimization process. The statistical optimization procedure used is the method of consecutive screenings. With this methodology, six factors are optimized: mass distribution of the fuel injection pattern, injection pressure, combustion phasing, EGR rate, boost pressure and dwell time between injection events.