For air quality, the Euro VI emissions regime is quite demanding: NOx is 460mg/kWh and tail-pipe particulate matter emissions are 10mg/kWh; both are measured in the transient, WHTC cycle. Three years before Euro VI, the USA’s diesel emissions regulations established by its Environmental Protection Administration were even more restrictive on air quality: 268mg/kWh for NOx and comparable levels to Euro VI for PM (13mg/kWh).
Future policies will curb the use of higher-polluting vehicles, especially diesel. Ricardo believes that post-Euro VI, statutory NOx emissions levels will be approximately cut in half, perhaps to 230mg/kWh in the WHTC cycle. In addition, there may be a new limit on the particularly harmful component of NOx, NO2, perhaps to 110mg/kWh in the WHTC, or to a maximum of 50% of total NOx.
Elsewhere, the developing world is catching up: India and China also have plans to introduce Euro VI-equivalent emissions restrictions, coming in 2020 in India, and starting next year in Beijing, to roll out nationwide from perhaps 2022. Industry has perhaps not received sufficient credit for achieving these levels of reductions. And the US state of California, which enforces its own emissions rules, may impose very low NOx levels soon, too. Levels of 134mg/kWh are currently only voluntary, but Californian authorities hope to make such ultra-low NOx standards mandatory in the early 2020s.
Reducing NOx levels can impact fuel consumption negatively. Ricardo estimates that systems required to reduce the EPA 2010 legislation levels by up to 75% might cause a 2% composite fuel penalty. Technology using NOx adsorbing catalysts can boost the reduction to almost 90%, but at the cost of a 3% penalty.
During a time of some geopolitical uncertainty, the diesel engine world is also unsettled, with the VW emissions scandal, and this summer’s announcements by Britain, France and China suggesting that they may ban diesel and petrol engines: the first two by 2040, the latter’s timescale is uncertain. Even diesel engine manufacturer Cummins announced plans to launch an electric truck recently, a demonstrator of which uses a 140kWh battery pack instead of 12-litre engine for a 100-mile range. A range extender model incorporates Cummins’ B4.5 or B6.7 engines, offering 50% fuel savings compared to today’s diesel hybrids.
So, it might be useful to consider then the strengths, weaknesses, opportunities and threats of the diesel engine for the next 15 years or so, to 2030. Its strengths include: low fuel consumption under typical road operating conditions; a low-cost, robust and durable design good for a million miles; the engine matches well to the SCR for efficient NOx reduction; and there is a well-defined existing fuel infrastructure.