From 2013 and beyond, additional emission regulations will go into effect. Compliance with these standards presents an ongoing challenge to all manufacturers of diesel engines. Marc Ostermann reports.
Text: New and tougher emission standards have been put in place to combat the affects related to the release of noxious nitrogen oxide gas (NOx) into the atmosphere by diesel-powered vehicles including trucks, busses, construction and agricultural equipment.
With engine optimisation options fully developed and implemented, new requirements can only be met through effective methods for handling and treating exhaust gasses.
In response, engine makers are utilising advanced technologies designed to meet the need and ensure compliance. The selective catalytic reduction system (SCR) has proved very successful in reducing emissions and thus has been accepted as the right answer versus other emissions technologies for the new EUR IV regulations that now start to come into place.[Page Break]
Selective catalytic reduction
A SCR system is comprised of a special catalytic chamber built into the exhaust system of a diesel engine. SCR uses a Diesel Exhaust Fluid (DEF) as a means of converting noxious nitrogen oxides (NOx) in engine exhausts into harmless diatomic nitrogen gas and water. In a typical SCR system, a 32.5 per cent aqueous urea solution (ADBlue) is injected into the hot exhaust gas. ADBlue is hydrolysed above approximately 180°C forming ammonia, which in turn reacts with the gas to produce harmless nitrogen and water.
ADBlue freezes at -12°C, therefore, conveying ADBlue fluid throughout the SCR system requires high-quality hoses designed for SCR applications. There are three hoses which circulate ADBlue throughout the system (tank supply line, tank return line, pressure line). It is critical that the hoses are able to heat the Urea solution quickly, heat uniformly throughout the hose assembly including the fittings, and optimise power consumption in the system.
Gates has therefore developed a design for SCR assemblies, the EPDM-based hose construction has a special carbon fibre sleeve and come with heated fittings (SAE J2044 compliant quick connect couplings). Thermoplastic over-moulds protect electrical connections against moisture and corrosion.
Additionally the SCR system (AD Blue supply tank) is also heated via the coolant circuit for which Gates is offering ECR (Electrochemical Chemical Resistant) EPDM hoses and which are colour-coded for easy selection and installation.[Page Break]
Optimal performance
The SCR system does not work until the fluid is thawed. Therefore if it takes x minutes to thaw the system, the vehicle will be operating for x minutes before the emissions are treated. The table below compares the performance of various SCR heated hose assembly designs out in the market. The time to thaw metric shows the comparison on how each design performs in the areas of power optimisation and fluid heating rate.
The SCR heated hose assembly heat uniformity is compared below for each design. The coiled wire designs result in an uneven heating pattern; therefore, resulting in a longer time to thaw. Gates carbon fibre braided sleeve design resulted in uniform heating throughout the hose assembly including the fittings. This resulted in the SCR heated hose assembly to thaw the ADBlue fluid quicker.
Also the protection of the connectors has been viewed as another important point for optimal performance of your SCR system. Field tests have proven that moisture ingression can cause SCR assembly failure, due to electrical connections corroding and eventually stop working.
With Gates thermoplastic over-mould design this concern is outruled. When subjected to salt spray testing per ASTM B390 for more than 18 months now, the assemblies have not had any change in electrical resistance which would affect the heating performance.
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Marc Ostermann is Engineering Director, Fluid System - Global Automotive & Transportation Systems, Dates Corporation, Englewood, CO, USA. www.gates.com/europe
Fig. 1. Include chart with implementation stages of EUR regulations)
Fig. 2. (SCR Truck Diagram.jpg) Include system sketch with different components in truck body)
Fig. 3. ( image001.jpg) Coiled wire designs.
Fig. 4. ( image002.jpg ) Carbon Fibre braided sleeve design.
