September 2019

BY Frank Massey W ith a focus on technical challenges and potential cost with diagnostic equipment and servicing, I think we should explore the technology that drives the need for specialist tools in both service and repair. I’m going to look at Euro 6 generation 2 diesel emission systems. I’m convinced that the more technology manufacturers throw at improving diesel combustion, the more problems they introduce. As usual, my knowledge is based on Volkswagen-Audi Group design. Engine design innovation is now closely following that of gasoline direct injection, alike to that of the EN888. MDB concept The VAG MDB concept engine design is a world based modular system. This allows for a more flexible production with regional variation based on local emission standards. The three basic modules are the intake systems, a central engine core based on the EN288, and the exhaust or emission module. The EN288 engine has 3-cylinder and 4-cylinder options with EU4/EU5/EU6 compliance. It is a cast iron block, alloy with the 3-cylinder variant, with and without balance shafts, crossflow alloy cylinder head with variable valve timing. A fully mapped and integrated coolant pump ensures maximum thermal efficiency. It important to understand that there are significant differences between the 2.0/1.6/1.4 3-cylinder and 4- cylinder design concepts, so various comments across the range of options will not reflect every variant. The 4-cylinder head has an offset valve layout. This introduces turbulence within the combustion chamber. The 3-cylinder valve layout is a conventional layout with swirl flaps in the intake module. Intake valve variation allows for a delay of intake valve closure (IVC) with a reduction of cylinder pressure during compression, reducing temperature and NOx. The control variator utilises oil pressure, with a backup accumulator to adjust IVO/IVC. Emission control module The emission control module is without doubt the most radical evolution. High pressure EGR is introduced via a valve directly from the exhaust manifold to the inlet, with the single aim of heating the 3way Euro 5 catalyst, or 4way Euro 6 catalyst when the engine is cold (see fig 1.) Low pressure exhaust gas passes via the EGR cooler, catalyst and particulate filter into the exhaust system. During NOx reduction strategies, exhaust gas is re- circulated aided by the EGR control valve and exhaust venturi or brake as it is referred to. This device partially closes the downstream exhaust circuit increasing upstream exhaust gas pressure by 30-40mb. This helps self-cleaning of the cooler and allows for AdBlue to be injected post cat pre DPF. Mixing is aided by the turbo. This also provides for the wideband NOx sensor to monitor NOx content before it enters the catalyst and particulate filter. The exhaust brake also increases the upstream exhaust gas volume through the cooler, aiding self-cleaning. In addition, the emission control module has the task of reducing ammonia NH3. Fuel delivery pressures have increased to 2000bar with delivery phases from 3/5/6 events depending on the operating profile. Additional combustion monitoring is achieved via a pressure sensor built in a heater plug. The sensor data helps the PCM calculate fuel quantity, timing and EGR values. There is also a feature I have supported for some time, relating to how the DPF is subject to regeneration or replacement based on saturation levels. Catalytic reduction 4-way catalytic reduction, co, hc, NOx, nh3. is based on principles of absorption followed by reduction (see fig 2). This is assisted with noble metals; platinum, palladium, and rhodium. An additional ingredient, namely barium, is used 24 AFTERMARKET SEPTEMBER 2019 TECHNICAL www.aftermarketonline.net EURO 6 SCR Frank looks at some of the challenges faced when dealing with the latest diesel engines Left: Fig 1 – High pressure EGR is introduced via a valve directly from the exhaust manifold to the inlet, with the single aim of heating the 3way, Eu5, or 4way Eu6, catalyst when the engine is cold Right: Fig 2 -4- way catalytic reduction, co, hc, NOx, nh3 is based on principles of absorption followed by reduction, this is assisted with noble metals, platinum, palladium, and rhodium