Technology and engineering experts recently presented technologies that enable diesel cars to achieve ‘near-zero’ emission levels.
The 40th International Vienna Motor Symposium which took place in May gathered engineering companies, the automotive supply chain as well as vehicle manufacturers to showcase their technological advancements in heavy-duty truck engines, cars and vans. During the event, participants looked at options for hybrid engines, fuel cells and future alternative fuels as well as important developments for petrol and diesel engines.
Importantly, the event showcased how the industry has developed powerful and robust advanced emissions control technologies for diesel engines, with the aim of achieving even lower emissions across the full range of operating conditions. As the European Commission starts to look at the next stage of vehicle emissions standards, several research teams have been taking different approaches to address the issue.
In order to demonstrate that the boundary conditions specified in today’s Real-Driving Emissions (RDE) legislation cover almost all foreseeable driving conditions and styles, it is important to understand how different people drive. One of the world’s largest automotive technology suppliers, Bosch, has been doing this. As a result, it has taken a whole system approach, looking in particular at improving and broadening control of nitrogen oxides (NOx), and at calibration and temperature control for the Selective Catalytic Reduction (SCR) functionality. While this has expanded the conditions under which the emissions control system is fully functioning in a demonstrator car, it has also been achieved at only ‘moderate additional cost’.
Under some of the most challenging test conditions, the car has easily met the current emissions limit of 80 mg/km. In slow urban driving around Stuttgart, NOx emissions even reached as low as 12 mg/km, close to what the company calls ‘near-zero air quality impact’. Based on these promising results, which build on work initially presented in 2018, Bosch concluded that diesel has the potential to meet future emissions limits which could bring urban air quality within permitted levels.
The automotive engineering company FEV configured a system with the exhaust after-treatment placed in front of the turbocharger. This resulted in higher temperatures and pressures in the system, allowing for smaller emissions-reducing catalysts. The system was complemented with a 48V mild-hybrid battery (read more in the box below) in a laboratory environment, which reduced CO2 emissions by 19%.
Different combinations of after-treatment layout were evaluated on simulated test cycles to replicate urban, motorway and rural driving. Under most of these conditions, NOx emissions were less than half of the current Euro 6 limits. Development work continues to bring down tailpipe NOx in the ‘extreme’ scenarios of city and motorway driving, even though it was already well within existing limits.
The event in Vienna was also the opportunity for the Association for Emissions Control by Catalyst (AECC), the International Platinum Group Metals Association (IPA) and the engineering company IAV to present the results of their programme that achieved ‘ultra-low’ diesel emissions. Similarly to Bosch, this collaboration carried out a range of real-world driving tests with a modified demonstrator car (see image below), a ‘mild-hybrid’ 2016 model. The car performed very well in conditions where NOx emissions are usually higher such as in the city of Berlin, on the German Autobahn with speed limits up to 160 km/h and in challenging hilly conditions.
Wanting to make best use of the whole system, AECC used a modular approach (see diagram below) when designing its after-treatment system. The first section of after-treatment technology in the exhaust converted NOx into harmless nitrogen in slow city driving, where engine and exhaust temperatures are relatively low. The second section enabled low emissions at higher temperatures, including those generated during fast motorway driving.
This was all made possible by enhancing catalyst functionality and improving engine control through calibration, with the 48 Volt mild-hybrid system enabling exhaust temperatures to be carefully controlled. This combination of technologies brought emissions to consistently less than half of the current NOx emissions limit, and often down to a near-zero level.
The video below demonstrates just how low the emissions are, thanks to this smart combination of existing components and technologies. The demo car cuts emissions at each stage of the emissions control system all the way up to the tailpipe.
Real-time analysis shows how NOx is reduced to near-zero levels at each stage of the emissions control system.
The AECC/IAV work demonstrated that NOx emissions from their demonstrator vehicle (green line) can be consistently reduced over a wide range of driving conditions.
The three research programmes from Bosch, FEV and AECC/IPA/IAV have shown that it is realistic to expect further improvements in emissions from modern diesel vehicles beyond what we know is coming to our roads over the next few years.
‘Near-zero’ is becoming a reality, making diesel cars future-proof and a key part of the vehicle mix for the next decade and beyond. Details of all AECC technical programmes and scientific publications can be found here.
Both AECC/IPA/IAV and FEV used 48 Volt mild-hybrid technology to boost the performance of their respective systems. For the former, temperatures could be controlled and each of the catalysts could function in optimal conditions. For the latter, it allowed for an electrical turbocharger to be used, compensating for the loss of pressure from having the exhaust after-treatment system in place. For vehicle manufacturers, 48V systems are a relatively cost-efficient way of improving efficiency. Unlike more expensive full hybrid systems where the battery takes over from the internal combustion engine to power the vehicle, for both petrol or diesel, a mild-hybrid unit is used to assist the engine by supporting various electric components on the vehicle. This helps with stop-start systems to reduce emissions in town centres and to recover energy during braking. It is estimated that about 16% of new diesel cars and 32% of petrol cars in Europe will be equipped with a 48V mild-hybrid unit by 2026.