Combustion engines impair the air quality in cities to a small extent. Emissions are also a by-product of the day-to-day operation of power stations and industrial facilities, to name just two sources. Diesel technology has reached a very high level of development, making the diesel engine one of the lesser factors that contribute to CO2 and particulate pollution. Bosch is working on reducing diesel’s contribution still further. Nitrogen oxide pollution will in the future likewise hardly be attributable to diesel.
The following charts show:
Our driving in everyday situations is multifaceted and includes acceleration, gradients, stop-and-go traffic, and high speeds, etc. The Real Driving Emissions (RDE) test procedure, which has been applicable since September 1, 2017, takes into consideration precisely these real-world driving conditions. In the past years, Bosch has actively supported the introduction of this procedure. After all, staying true to its guiding principle of “Invented for life”, Bosch is highly committed to using technologies that conserve our natural resources to the greatest extent possible. With RDE, the emission values are no longer measured in the test bay but instead under real driving conditions without a predetermined driving profile.
The specifications for conducting an RDE test drive include:
With RDE, it quickly became apparent that a more realistic consideration of real-world driving leads to more relevant solutions. At Bosch, the many new insights have accelerated technological development significantly. Bosch engineers have succeeded in achieving average NOx emissions of 13 mg/km on RDE-compliant test drives with urban, rural, and freeway elements. This means that with the current state-of-the-art exhaust technologies from Bosch, vehicles are already today able to achieve significantly lower emissions than the EU’s NOx emission limit of 120 mg/km that will be applicable from 2020. And not only that: these reductions can be achieved using existing technologies and while preserving the diesel engine’s renowned efficiency. Bosch has been able to demonstrate ways in which the entire powertrain system can be optimized, achieving results that even exceed Bosch’s own expectations. Bosch makes this possible with, for instance, a rapid-response air management system and sophisticated thermal management of the exhaust-gas treatment system. Regarding the air management system: the more dynamic the driving style, the more dynamic exhaust gas recirculation must be as well. Turbochargers that respond more quickly than before meet these requirements. The combination of high- and low-pressure exhaust gas recirculation makes the air management system even more flexible. And regarding the sophisticated exhaust-gas treatment system: Bosch has found a solution in which the starting temperature barely has an effect on emissions anymore.
Up to now, an issue had existed where – under certain driving conditions – the temperatures in the exhaust system could sometimes drop to a level that was too low, which meant that proper functioning could no longer be fully ensured. By establishing a smart link between the engine and exhaust-gas treatment system, it is now possible to take corrective action with foresight. This ensures the exhaust system stays warm enough and can do its job reliably, even in city driving.
An external engineering company analyzed the emissions data collected at the Neckartor in Stuttgart, one of the most critical spots in the whole of Germany. After applying a variety of computational models, it came to the following compelling conclusion: if diesel vehicles equipped with the latest technologies replaced the current diesel fleet, the diesel engine would only be responsible for a negligible portion of the relevant emissions. The analyses showed that a reduction in the average nitrogen oxide readings had been achieved on the urban RDE test drives in Stuttgart: from 90 mg/km in 2016 to 80 mg/km in 2017. And in 2018, this was reduced still further – down to 40 mg/km. Bosch has therefore come closer to achieving the goal of a combustion engine that no longer significantly pollutes the air. And that is a revolution for the now more than one-century-old diesel engine.
Diesel injection system CRS3-27 for a maximum pressure up to 2,700 bar
Rotational speed measurement for greater engine power output
Diesel exhaust fluid metering system to reduce nitrogen oxides (NOx)
RDE is the right step towards greater transparency in terms of emissions. There is, however, also a need for more clarity when it comes to measuring fuel consumption too. The current measurement method leaves a gap between certified consumption and actual consumption. With the on-board measurements planned by the EU, a clearer picture of the actual fuel economy and thus also of the CO₂ emissions will soon emerge. Bosch is going one step further and is calling for Real Driving Consumption to be used as a benchmark so as to achieve even greater transparency with regard to the carbon footprint of vehicles. The more effectively CO₂ emissions can be measured, the more clearly necessary measures can be defined. Bosch is therefore advocating a comprehensive carbon footprint for vehicles – one that is “well-to-wheel” and not just “tank-to-wheel”. Well-to-wheel encompasses the entire causal chain comprising the extraction, supply, and conversion of energy. In terms of the comprehensive well-to-wheel carbon footprint, the combustion engine and electric drive are not as far apart as is generally assumed. One advantage of this approach would be that non-fossil fuels, like paraffinic fuels, can be taken into consideration too.
These fuels are made from animal and vegetable waste. Already today, they can be used as an additive of up to 30% volume in blended fuels and could reduce the carbon footprint by up to 25%. As a result, when considered well-to-wheel, the carbon footprint of a modern diesel vehicle would be almost halved with such fuels – from the current 110 g/km to 60 g/km. In the well-to-wheel analysis for electric vehicles, the production of the electric power is also included in the carbon footprint calculation. Based on the mix of energy sources currently used in Germany for electric power generation, a compact electric car likewise has a carbon footprint of 80 g/km – and when considered in terms of the European mix, the footprint is still 40 g/km.
It is evident that both technologies are ready for a more environmentally friendly future. Though to achieve that, more renewable power is needed for the electric drive and more reduced-carbon fuels are required for the combustion engine. With synthetic fuels (eFuels) there is even the prospect of running the combustion engine with a net zero carbon footprint. Bosch will continue to press ahead with the development of environmentally friendly powertrain systems to further improve air quality.