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Bosch announces RDE-optimized, low NOx diesel engine technology

25 April 2018

Robert Bosch GmbH announced a diesel engine control strategy that can reduce NOx emissions from diesel cars under real driving conditions to well below the applicable EU regulatory limits. The technology involves a combination of advanced fuel-injection, a newly developed air management system, and “intelligent” exhaust gas temperature management. There is no need for additional hardware, as the technology is based on components already in use in production vehicles.

“There’s a future for diesel. Today, we want to put a stop, once and for all, to the debate about the demise of diesel technology,” said Volkmar Denner, Bosch CEO. “Diesel will remain an option in urban traffic, whether drivers are tradespeople or commuters.”

Since September 2017, new EU passenger car models are subject to real driving emissions (RDE) testing, which involves driving the vehicle over a mix of urban, extra-urban, and freeway cycles in real traffic. RDE emission limits are defined by multiplying the respective NEDC emission limit (80 mg/km for NOx) by a conformity factor (CF). The current CF for NOx is 2.1 (Euro 6d-TEMP) and the corresponding RDE NOx limit is 168 mg/km. From 2020, the CF for NOx is to be lowered to 1.5 (Euro 6d) and the corresponding NOx limit to 120 mg/km. Vehicles equipped with the new technology driven by Bosch could achieve NOx emissions of as little as 13 mg/km in legally-compliant RDE cycles. When driving in particularly challenging urban conditions, where test parameters were in excess of legal requirements, the average NOx emissions of the Bosch test vehicles were 40 mg/km.

The new Bosch strategy is a highly responsive air flow management system for the engine that can provide a dynamic recirculation of exhaust gases. This is achieved with the use of an RDE-optimized turbocharger that reacts more quickly than conventional turbochargers. Further flexibility is achieved through a combination of high- and low-pressure EGR. As a result, drivers can drive off at speed without a spike in emissions.

Another important component of the new strategy is the exhaust gas temperature. To ensure optimum NOx conversion in the aftertreatment system, the exhaust gas temperature must be above 200°C, said Bosch. This temperature is not always reached in urban driving, when cars are operated in gridlock or stop-and-go traffic. The new technology includes a sophisticated thermal management system, which actively controls the exhaust gas temperature to ensure the exhaust system stays hot enough to function within a stable temperature range. Some components of the thermal management include fuel injection timing (e.g., retardation) and pattern (e.g., late post injection) to warm up the aftertreatment system, as well as air flow control to keep the aftertreatment within the target temperature range. It is unclear whether an electric heater is also used, but the technology does not require a 48V onboard electrical system.

These NOx reduction measures do not significantly impact fuel consumption, said Bosch, but no figures were given. Some more technical details are expected to be available in a technical paper presented by Bosch at the Vienna Motor Symposium.

Bosch also called for a renewed focus on CO2 emissions, which are directly related to fuel consumption. Fuel consumption tests should be conducted under real driving conditions, like RDE emission tests, and vehicle CO2 emissions should be assessed on a well-to-wheel basis, extending significantly further than the fuel tank or the battery. “We need a transparent assessment of the overall CO2 emissions produced by road traffic, including not only the emissions of the vehicles themselves but also the emissions caused by the production of the fuel or electricity used to power them,” said Volkmar Denner.

The new diesel system is available to customers effective immediately, said Bosch, and can be incorporated into production projects.

Source: Bosch