Evolutionary process

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European Union legislators have placed considerable emphasis on particulate matter (PM), including ultra-fine particles, and NOx reductions in Stage V. This is set against a backdrop of increasing evidence of the damaging health effects of these pollutants in diesel exhausts.

Ultra-fine particles within PM are a serious concern because research has shown that they cause damage to the heart and lung when inhaled. Stage V, therefore, introduces a particulate number requirement, as well as further reductions in PM mass not only for engines previously regulated at Stage IV, but a wider range of engine powers. For the first time this effectively mandates the use of diesel particulate filters (DPF) or a SCR coated DPF.

Table 1: Stage V proposed emission limit

As shown in the table above, Stage V requirements, when they become mandatory between 2019-20, will introduce stringent emissions standards for a widened scope of engines. These include compression ignition (CI) engines below 19kW and all engines above 560kW, which were previously outside legislative requirements.

Stage V therefore covers a much greater variety of machinery, from small gardening equipment such as lawn mowers and chain saws, through to larger construction plant machinery. So, new to Stage V compliance will be powered wheelbarrows, small dumper trucks, scissor lifts and remote power generation, as well as many others powered by engines less than 56kW – the list is extensive. Agricultural machinery and large engines used in railcars and inland waterway vessels are other examples of larger engines that will have to comply with Stage V.

Despite the challenges presented by the addition of larger and smaller engine sizes and new emission targets, compliance with Stage V does not require a revolution in terms of exhaust aftertreatment. Indeed, much of the technology already exists – as in the case of diesel particulate filters (DPF), which are widely used by our OE customers to meet current Euro VI legislation for heavy-duty vehicles.

Stage V challenges

Smaller engines present a number of specific challenges with wide temperature variations in the exhaust pathway requiring a well-planned approach to thermal management. In these instances, various options will be explored, such as: close coupling a compact SCR coated DPF with the engine; or chassis mounting a high-efficiency SCR catalyst, with low light-off temperature, and DPF complemented with advanced insulation on the entire system to retain the exhaust temperature.

On larger engines, the use of high-flow injectors is necessary to deliver the required volume of AdBlue into the SCR system to trim NOx. Specific attention needs to be given to tuning the spray pattern, ensuring fine atomization for better mixing, minimizing wall wetting and eliminating crystallization of urea on the injector nozzle.

In both of these situations – large and small engines – we have evolved our technology to meet the design, spatial and technological challenges that Stage V will present. This has been helped by the fact that we have developed solutions for on-highway Euro VI engines in recent years

Naturally, balanced against these many technical demands is the need to provide a value for money exhaust after treatment system (EATS). This is brought into perspective when you consider the potential cost of developing a Stage V compliant solution for a 19kW engine from scratch, which OE manufactures in the newly-regulated engine size bandings are potentially facing.

There are obvious timescale and value engineering advantages to evolving a solution from technology and components that already exist. Creating it from a blank sheet of paper and apportioning these development and toolings costs to the finished product would potentially price the engine (and product) out of the market. Plus, an ‘evolved’ approach ensures a fast route to market, which not only reduces the overall project cost but maximizes the commercial opportunity for OE manufacturers.

So, in summary, we can see that despite a number of challenges, compliance with Stage V doesn’t have to be a revolution in exhaust aftertreatment design – but an evolution of existing expertise.

June 23, 2015

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