Temperature in the aftertreatment unit is key to the reduction of emissions and its management can be difficult. Baumot solved that problem with a compact unit that is suitable for both coach and bus use
Retrofit to Euro 6 standard is generally straightforward for popular bus models, and its development has been propagated by public money. For coaches, no such clarity or external support exists, although identical technology will be used.
Baumot has developed a patented system that suits both sectors. Called the BNOx ammonia generator, it reduces NOx and particulate matter (PM) emissions to far below what is legally required at Euro 6.
One of the system’s key benefits is an ability to function fully in low-speed traffic where exhaust gas temperatures are typically well below 200oC. It thus delivers optimum performance at all times and it can upgrade engines from as far back as Euro 3.
Generating ammonia by heating AdBlue and injecting it into the exhaust aftertreatment unit is a clever yet simple principle. The consistent emissions reduction performance that delivers is the central point when upgrading older engines to better than Euro 6 standards.
“Low temperatures under urban driving conditions in Euro 4 and Euro 5 exhausts is why their SCR systems often don’t work properly,” says Twintec Baumot MD Bert Pierlings.
Baumot’s system addresses that. It does not rely on heat within the exhaust gas to function. Instead, it uses a high temperature within the ammonia generator.
“To create ammonia, we take hot pre-turbo exhaust that is fed to the generator. A minimum of 220oC is required, and with the additional presence of an electric heater, that is guaranteed,” he continues. Within the aftertreatment unit, the ammonia generated reacts with the main exhaust gas feed with the help of catalysts to massively reduce NOx and PM.
“In a nutshell, our system delivers the same emissions reduction performance at low temperatures as it does when the engine is worked hard,” says Mr Pierlings.
The technical bits
The ammonia generator is the size of a drinks flask. Baumot mounts it in a suitable place within the engine bay that is not susceptible to damage and, subject to the intensity of the operating cycle, it is sealed for at least four years. The aftertreatment unit has no additional space claim over the OE installation and it includes a diesel particulate filter.
How the ammonia enters the aftertreatment unit is important. Baumot has done much work to ensure that it happens well ahead of the SCR catalyst and the ammonia’s even distribution. Otherwise, NOx reduction would be compromised and the system would lose effectiveness.
Various Baumot-supplied brackets go with the ammonia generator and the exhaust unit. It installs an AdBlue dosing system and the equipment required to take a pre-turbo exhaust gas feed. Piping to connect everything together is also provided.
The remaining components are electrical. The ammonia generator’s heater runs from a 24v feed and there is a control unit. Additionally, a NOx sensor is fitted at the end of the exhaust, and for good reason.
“A telematics box is part of the installation,” says Mr Pierlings. “It transmits data including NOx reduction, AdBlue tank level and exhaust back pressure. If back pressure rises, it indicates that the DPF needs cleaning.”
Regardless of how effective the emission reduction process is, ash still accumulates in the DPF. The majority forms from oil, and it cannot be burned off. Older engines consume more oil than newer units, and thus vehicles with them require more frequent DPF cleaning.
Baumot promises no more than a 1% fuel consumption penalty. Tests have shown that the BNOx ammonia generator delivers a 99.8% reduction in NOx, fewer than three parts per million ammonia slip, and below 40 millibars of back pressure.
“That makes PCVs with our BNOx ammonia generator incredibly clean,” says Mr Pierlings. Baumot believes that the unit takes a diesel engine to as close to zero emissions as is possible, but to satisfy the UK’s retrofit certification requirements, such performance is necessary. “They are the most stringent that I have seen. They are above even what Germany mandates. Some elements are higher than Euro 6 OE standards.”
Baumot has achieved certification for all Alexander Dennis Enviro200 and Enviro400 models at Euro 5 under both the Transport for London (TfL) and the nationwide test cycles. The latter involves more higher-speed running.
It has also gained TfL and nationwide certification for the Cummins-engined Optare Solo and the Wrightbus StreetLite, and for the Euro 5 Scania DC-09 EGR engine in both double- and single-decker chassis. The Volvo B9TL has likewise passed the TfL cycle at Euro 5. Subject to demand, more models will follow.
The process surrounding fitment is tailored to the operator’s requirement. Baumot is establishing a network of trained service partners that can carry out the work at depots, or it can fit the equipment at its Silverstone headquarters.
The first of these partners is Leyland-based MI Vehicle Integration, which will also be established as Baumot’s Coach Development and Service Centre. More partners will be added, but the selection process is rigorous.
“They are specialist coach and bus engineering companies,” says consultant Alan Martin. “We are in discussions with five others.”
Technicians at its partners will be trained by Baumot. They will then work with one of Baumot’s own engineers until they are fully competent. Even when the kit has been fitted by a partner, Baumot takes responsibility for service and support.
Prior to the installation, it’s necessary for a vehicle health check to take place. The engine and turbo must both be in good condition and there can be no oil leaks. There must also be no modification from the OE specification.
A hurdle that is slowing the addition of further bus models to the existing list of certified vehicles is securing the use of testing facilities. That may also impact coach certification, but Mr Martin says that there is a potential partial resolution.
Coach retrofit on track?
Coaches represent smaller volumes than buses. But the BNOx ammonia generator is perfectly suited to coaches and Baumot will develop applications for more common models; a Volvo B9R is at Silverstone to start that process.
“We have an agreement in place with a coach supplier to retrofit vehicles, but the waters are not clear,” says Mr Martin. Low-volume conversions can be achieved, but the cost of doing so will be higher.
Coach retrofit may, as already suggested, come to involve certification of an engine and aftertreatment unit combination that, subject to compliance, can be ‘read across’ other vehicle models. Alternatively, it may utilise a vehicle-mounted portable emissions measurement system (PEMS). “At the moment, the unknown for coaches is how the testing will be carried out. It is quite a ‘hot potato’,” he adds.
Should PEMS certification be accepted, Baumot will be able to move quickly. “We need to know the testing parameters, but we have the equipment and we are ready to go with PEMS.”
A further outstanding question about coach certification is how ongoing compliance will be managed. Telematics data will be available; whether it will be required or not is unknown, as is who the overseeing body will be if it is mandated. “We see potential in coaches. We haven’t identified any PCV that our equipment will not fit. But there has to be a compromise, and soon, if any coaches are to be certified in time for London’s ULEZ,” concludes Mr Martin.
All of Baumot’s retrofit systems are provided with a two-year warranty and support package, which can be extended to five years at additional cost. It can also offer finance in partnership with Mistral Asset Finance.
Temperature management within exhaust aftertreatment units has been the Achilles’ heel of emission reduction. Unlike OEM Euro 6 installations, where engines have in some cases been downsized to address the issue, retrofit suppliers must deal with what they are given.
Baumot’s use of an ammonia generator is key to the BNOx system. By removing the point of temperature criticality from the exhaust and instead using a smaller and much more easily controlled heater, it can guarantee emission reduction performance.
Baumot is also the second aftertreatment specialist in as many weeks to publicly question whether any coaches will be retrofitted and certified in time for London’s ULEZ.
It looks increasingly likely that none will be, but that is not for lack of trying on the part of suppliers. As has long been the case, politicians are preoccupied with buses while coaches are forgotten about.