Have we found the future of diesel technology? John Kendall investigates the next generation of diesel engines.
Just as buyers are getting used to the latest Euro five engines, the manufacturers of fuel injection and emissions control systems are already well advanced on the next phase, Euro six, which is just under three years away. Although the regulations do not call for a further reduction in particulate matter (PM) for diesels, emissions of oxides of nitrogen (NOx) must be cut by 55 per cent and at the same time, car manufacturers must also reduce the fleet average carbon dioxide emissions to 130g/km by 2015, meaning that fuel consumption must also be reduced, too.
For both fuel injection and exhaust aftertreatment manufacturers, there’s work to do and further integration between injection and aftertreatment is also important. Bear in mind that there are a few basic rules concerning diesel exhaust treatment. When it comes to balancing NOx and PM emissions, the engine maker can reduce one in the combustion process but this tends to increase formation of the other in the exhaust, which means that if you treat NOx formation in cylinder, you must treat PM in the exhaust and vice versa. Euro five required both to be reduced. Historically, car makers have worked on reducing NOx in cylinder and treating PM with exhaust gas recirculation (EGR) and a diesel particulate filter (DPF) in the exhaust. Come Euro six, how will it be done? With such tight limits, it seems likely that many manufacturers will treat the exhaust for both NOx and PM. We caught up with some engineers from Delphi, which makes both injection and aftertreatment systems, at the Frankfurt Motor Show to find out.
Firstly, we can expect to see injection pressures rise, as John Fuerst, Managing Director of Delphi Diesel Systems explains, “for fuel economy, diesel already has an advantage, but you can get more power out with higher fuel injection pressures, and you can help yourself on emissions with higher injection pressures.” Delphi systems are currently operating at 2,000bar and the company is looking to the 2,200 to 2,500bar region for Euro six and beyond.
“The problem is when you do that, you make more NOx and so we’ve got an SCR (selective catalytic reduction) product that’s high pressure and water cooled”, continues John, “then at the component level there’s durability issues, we’re working on our components to make sure that it works with global fuels and global markets – we’re in production and shipping into India and China. In our injector for example, our very small valve, which makes us very fast and precise, is more susceptible to bad fuel and sticking or clogging, so we’re continuing to develop and improve it to make sure that the spring strength and coil strength together with coatings and everything else makes sure that that valve is always operating optimally.”
Treating NOx as well as PM in the exhaust involves using AdBlue, a urea based additive injected into the exhaust stream or alternatively using a solid additive in the exhaust system. Delphi has opted for a higher pressure SCR dosing system; as John explains, “It provides better distribution, better mixing and more uniform distribution of urea across the face of the catalyst, which gives better performance.” The system injects AdBlue at over 20bar to achieve these effects.
Where is diesel technology heading post Euro six? “More pressure, lighter weight and more efficient and better combustion through superior control,” reckons John.