Ammonia creation and conversion technology cleans up diesel

In an era of increasingly strict emissions regulation, ammonia creation and conversion technology (ACCT) extends the operation of selective catalytic reduction systems to low-temperature exhaust conditions

The toxic cocktail of tailpipe emissions has been closely regulated since 1993, when the EU introduced Euro 1, a set of mandatory standards designed to put OEMs on the road to cleaner vehicles. In the space of 24 years, increasingly stringent standards have led to reductions in the permissible limits for carbon monoxide, hydrocarbons, particulate matter (PM) and oxides of nitrogen (NOx), while ongoing efforts seek to further reduce their impact.

At a regional level, London is seeking to redress the situation with the introduction of a T-Charge (or Emissions Surcharge), which requires drivers of pre-Euro 4 cars to pay £10 to travel to the city’s central zone. According to the Mayor of London’s office, 7.9 million Londoners – nearly 95 per cent of the population – live in areas exceeding the World Health Organization guidelines on toxic air quality particles (PM2.5), and air pollution contributes to thousands of premature deaths in the capital each year.

In July 2017 the UK government announced plans to improve air quality – and, by its calculations, recoup billions of pounds in lost productivity – by tackling roadside concentrations of nitrogen dioxide. One of the ways it will do this is by ending the sale of all new conventional petrol and diesel cars by 2040. The government acknowledges that Britain is among 17 EU countries in breach of annual targets for NO2, but it lays some of the blame – with a degree of justification – at the same European testing regime that sought to curb harmful emissions.

The focus on cars, however, overshadows the regulations as they apply to other modes of on- and off-road vehicle. In 2014, European Regulation UN ECE 595/2009 brought in the Euro 6 standard for heavy-duty diesel engines, reducing the limit for NOx emissions by 77 per cent, while continuing to set challenging limits for the control of other gases and particulates. According to Transport for London, the test protocol changed to broaden the range of speed/load conditions for which an engine had to meet the emissions limits. Additionally, an ammonia (NH3) concentration limit of 10ppm now applies to diesel and gas engines, which was introduced to control ammonia slip from selective catalytic reduction (SCR) systems used to control NOx emissions.

However, by the time Euro 6 was introduced in January 2014, a public-private partnership was already more than a year into a project aimed at ensuring the viability of on-highway vehicles and heavy-duty diesel vehicles (HDVs) in an era of increasingly strict regulation. The effort marked the first collaboration between Loughborough University and the Energy Technologies Institute (ETI), which commissioned the project as part of its Low Carbon Heavy Duty Vehicle (HDV) Programme. ETI’s focus on HDV efficiency was prompted by the limited options for low-carbon fuel alternatives for HDVs, plus the fact that the proportion of CO2 emitted by HDVs would continue to rise relative to other sectors. The HDV programme – incorporating land, sea and rail vehicles – identified efficiency as the most cost-effective way of reducing emissions and set a target to improve HDV efficiency by 30 per cent.

As part of the overall project, UK-based specialist teams from ETI member Caterpillar and Johnson Matthey have worked on novel SCR technology to help achieve the 30 per cent target and 3-4 per cent fuel-efficiency improvements.

Research at Loughborough has further improved SCR, with the development of its own ACCT (ammonia creation and conversion technology), a highly novel device that extends the operation of SCR to low-temperature exhaust conditions. As well as lowering NOx, ACCT could deliver fuel savings. Loughborough’s Prof Graham Hargrave developed the technology with research associate Jonathan Wilson.

In May 2017 Hargrave said that many engines – such as those used on buses and construction vehicles – never reached the optimal temperature required for SCR systems to operate efficiently because of the stop/start nature of their journeys. The SCR systems themselves treat NOx emissions with AdBlue, which provides the ammonia required to reduce NOx into nitrogen and water. According to Loughborough University, AdBlue functions well only when temperatures exceed 250ºC, so the SCR does not necessarily operate in all engine conditions, such as stop-start commutes. Similarly, at lower temperatures the use of AdBlue can result in severe exhaust blockages and subsequent engine damage.

The ACCT technology, a world first, has been tailored for HGVs but the same system is fully scalable for use in all diesel vehicles. More broadly, the project has delivered 21 innovation notifications, seven patents and a series of new models for after-treatment design. The patents include the SCR after-treatment injector/mixer concept, the exhaust architecture, new sensors and novel control approaches.

A further patent has been submitted under the Green Channel accelerated scheme for ACCT. According to Loughborough marketing manager Anna Leather, the overall project presented a range of challenges, not least the need to strike a balance between the interlinked requirements for legislation relating to NOx emissions and CO2 reduction, lower fuel consumption and engine efficiency for the consumer, and the performance and cost concerns of the manufacturer. The project therefore required a multi-disciplinary approach in which each partner was assigned key reporting responsibilities alongside their expertise. Individual responsibilities were also assigned within the control system, catalyst and applied research teams, with an agreement to share key decisions as each parallel work package progressed to inform the next project phase. This resulted in it being delivered on time, in budget and meeting legislative, consumer and manufacturing requirements.

With the project now entering the exploitation phase, the ETI’s influence in engaging government and industry is crucial to the rollout of this groundbreaking technology. It is also engaged with several OEMs that may wish to exploit the technology, including the ACCT device, for on-highway application.

As first adopter, Caterpillar has produced a demonstrator vehicle to showcase the efficiency improvements for the off-highway HDV application.

The potential environmental, societal and economic impact of this project is significant given that trucks, buses and coaches produce about 25 per cent of CO2 emissions from road transport in the EU, and some 5 per cent of the EU’s total greenhouse gas emissions.