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CLEANER GREENER
Page 54
Page 55
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As we prepare for Euro-4 in 2005, ArvinVeritor has unveiled a system that could knock EGR and SCR for six. Brian Weatherley reports.
Tnick manufacturers and buyers will have to meet even tougher emission challenges when the Euro-4 exhaust standard comes into force on October 2005. And when it comes to reducing emissions, engine designers have a simple choice: exhaust gas recirculation (EGR), or selective catalytic reduction (SCR). Euro-4 is so strict that they can no longer tackle the problem of NOx, CO,HC and particulates (soot) within the combustion chamber alone; the only way out is exhaust after-treatment.
While most US manufacturers (under pressure from the Environmental Protection Agency to do something about exhaust emissions PDQ) have gone down the route of EGR many European manufacturers have leaned towards SCR with others, including Scania, 'picking and mixing' their after treatment technology depending on the engine. For example, on Scania's new R Series all Euro-4 straight-sixes will have EGR, while its mighty V8s will come with SCR.
The pros and cons of EGR vs SCR have been pretty well aired, not least in CM,15 January, where we looked at all the operating factors of both systems.
In a nutshell, while EGR is low-risk' technology, having already been in use for a while, service intervals, and in particular oil change periods, invariably take a hammer ing. Conversely while SCR offers the chance to run an engine "dirty", and then tidy it up in the catalytic process,thereby gaining fuel economy benefits of up to 7% over EGR,it involves a whole new set of kit for the truck.Tbis includes dosing units and separate urea tanks as well as the infrastructure needed to run an SCR-equipped truck nationwide. It's a choice all right, but not a very good one.
However, US component manufacturer ArvinMeritor has thrown its hat into the low emissions ring with what it calls its Plasma Fuel Reformer Enabled NOx Trap. Originally developed by the Plasma Science and Fusion centre at the prestigious Massachusetts Institute of Technology, this system uses an electrical "plasma", or strong continuous spark, to partially combust a mixture of air and diesel in a unit downstream of the engine. There's insufficient air in the unit to create full combustion, so instead of burning the fuel breaks down into a hydrogen-rich gas.'This is then fed into a NOx trap in the exhaust system where the oxides of nitrogen are combined with the hydrogen to produce harmless water vapour and nitrogen which then pass out of the exhaust normally.
According to ArvinMeritor the Plasma Fuel Reformer can supply hydrogen to the NOx trap at any time, from any hydrocarbon fuel, including petrol.The firm claims: "Over the long-term the hydrogen-rich gas may also be used to greatly enhance the combustion efficiency of gasoline engines."
Like SCR,it allows the engine timing to be advanced for maximum fuel economy while handling the higher levels of NOx. But, unlike SCR systems there's no need to refill a separate tank with urea in order for it to work and you don't need to store hydrogen either, as it's available "on demand".
Other benefits include weight savings — US industry insiders say the prototype plasma generator is no bigger than a standard US "coffee can-, which makes it significantly lighter than an SCR system.This would free up a tractor chassis for other more important things like diesel tanks (the production model generator would probably be sited somewhere between the truck's diesel tank and NOx trap).
The plasma generator also has a low electrical drain on average less than 100 watts on the prototype, with production versions expected to be even lower-so there's no need to beef up the truck's battery and charging system.
Wide temperature range ArvinMeritor reckons its prototype Plasma Fuel Reformer regenerates a NOx trap using about half the amount ("and even less in some conditions-) of diesel consumed by conventional Active Regeneration' particulate traps which use diesel to burn off the collected soot. What's more,it operates effectively over a broader engine temperature range,notably at lower temperatures and even when the engine is idling.
Fmally,ArvinMeritor says:"Prelimiriary lab tests show the ability to successfully remove sulphur from the NOx absorber at temperatures well below 500°C, enabling long life of the catalyst system itself." However, that's probably more important in the US where operators still run with relatively high levels of sulphur in their fuel: this September the UK sulphur limit will be cut to 10 parts per million. Compare that with the 50ppm limit in ultra low sulphur diesel in the run-up to Euro-4.
The good news is that ArvinMeritor is now offering a "third way" on exhaust treatment; the bad news is the Plasma Fuel Reformer won't officially go into full production until 2010.The company says:"Aggressive in-vehicle testing is now under way in 'real-world' applications of hydrogen-enabled after-treatment systems on heavy and light trucks and buses." In other words there's still a long way to go.
The 2010 launch date is not exactly a coincidence; the US will adopt even tighter exhaust standards that year to replace the regulations due in 2007. Its timing will also be of great interest to European manufacturers facing the Euro-5 standard in 2008. own into a Whatever its final arrival date, there's no doubt that all the major engine manufacturers will want to discuss the Plasma Fuel Reformer with ArvinMeritor, which states somewhat grandly:"The company is poised to assist engine, truck and automotive manufacturers in meeting what is likely to be the biggest environmental challenge of our generation." The biggest challenge will be to make it a truly viable alternative to SCR and EGR. If it can do that the sky's the limit for ArvinMeritor.•