Truck and bus diesel engine development has a long way yet to go, despite rapidly accelerating demand for electrification and growing popularity of alternative fuels such as natural gas.
This is the gist of a message Cummins is preparing to deliver next month at the huge IAA (Internationale Automobil-Ausstellung) commercial vehicles show in Hannover, Germany.
The point was underlined this month at the Cummins group’s Turbo Technologies division base in Huddersfield, West Yorkshire with the unveiling of a novel design of exhaust aftertreatment, designed to cut future diesel engine emissions of oxides of nitrogen (NOx) below even current stringent Euro VI limits, without sacrificing fuel economy in the process.
The familiar exhaust aftertreatment equipment fitted to nearly all the latest (Euro VI) diesel-engined trucks comprises a diesel oxidation catalyst (DOC), diesel particulate filter (DPF) and selective catalytic reduction (SCR), all housed with an exhaust silencer in a single box.
Exhaust after-treatments struggle to stay warm
Many elements of this equipment, especially the DOC and SCR, need to reach a high working temperature before they become most effective. The normal mounting position, outside the engine compartment and some way downstream in the exhaust system, makes it difficult for this high temperature to be reached, especially when the truck engine is working under light load in low ambient temperatures and the exhaust gas temperature thus stays low.
Truck manufacturers are under intense pressure from operators and legislators to improve fuel economy further and thus cut emissions of carbon dioxide. The upshot is that truck aerodynamic efficiency is being improved and engine speeds, on long-haul operation in particular, are being cut.
This means it is becoming increasingly difficult to raise SCR and DOC working temperatures quickly to where they need to be and then keep them there.
The close-coupled unit
One novel solution to this problem being put forward by Cummins is what it describes as a “close-coupled unit”. The essence of the idea is to mount the single-box exhaust after-treatment equipment (made by the Emissions Solutions operation in the Cummins Components division) much closer to the engine’s turbocharger (made by the division’s sister Turbo Technologies operation) in the engine compartment.
When this close-coupled unit works in tandem with the latest fixed-geometry Cummins turbocharger with a rotary turbine control instead of a conventional wastegate and with a new Cummins urea injector for the SCR system, the result is that exhaust gases entering the SCR can be as much as 70 degrees Celsius higher than with conventional after-treatment systems.
This, in turn, means cuts in NOx emissions without any sacrifice in fuel economy and emissions of CO2, according to Jonathan Wood, executive director of research and engineering at the Emission Solutions operation in the UK, based alongside the Cummins diesel engine manufacturing plant in Darlington, County Durham.
Until about a year ago, Wood had a similar research and engineering job at the Huddersfield Turbo Technologies plant. He says that his move is one of many examples of how the two divisions in the Cummins group are working more closely together than ever to solve the latest challenges facing all diesel engine manufacturers.
Cummins itself is one of the largest of these, producing around 1.3 million engines annually. Does it not fear this business has no long-term future, given all the latest anti-diesel sentiment from politicians and the public?
The short answer is no, though Wood is at pains to emphasise that Cummins long ago recognised the fast-growing demand for alternatives to diesel, especially pure-electric drivetrains. Hence its recent acquisition of UK-based Johnson Matthey Battery Systems and of Efficient Drivetrains and Brammo in the US.
Preparing for electrification
“Electrification is certainly coming,” says Wood. “There is no question about it. It is here. It is now. And we are absolutely in there. Speed of adoption will be fast in some sectors, slower in others. But diesel is still part of the picture, so we have to work on driving the performance and capabilities of diesel so it can remain an option.”
Wood promises that much more will be revealed about the latest Cummins plans for alternative fuels and electrification in particular at the Hannover show next month.
Tracy Embree, president of the entire Cummins Components division, is his boss. “It is an exciting time to be in the power industry,” she says. “Customers are demanding power options that deliver greater efficiency, reliability and flexibility, with reduced emissions.
“As engine manufacturers race to meet the demand for new power solutions, we are seeing new concept systems and innovations shaking up the industry, and we’re proud to be at the forefront of these developments.
“We are addressing this shift in the market by expanding our portfolio of products to reflect the needs of the future. In order to meet challenging new environmental guidelines, we’re adapting engine technology to meet the most recent emission standards, resulting in diesel engines that are cleaner, simpler and more efficient.
“At IAA we will reveal the new technology that we believe will future-proof diesel engines for the next generation.”