Increasingly stringent emissions legislation has seen many developments in engine technology and exhaust after-treatment over the last few years.
The market has been led by the more visible on-highway sector – trucks and buses, but off-highway plant has been following along behind.
While our cars are taxed on their output of harmful CO², heavy diesel engine emissions are regulated for particulate matter (PM) and nitrogen oxides (NOx), measured in g/bhp/hr or g/kW/hr.
Things have certainly come a long way. Just 30 years ago, one on-highway truck produced the same level of PM as 50 of today’s goods vehicles. By 2013 that level will have been cut by a further 50%. Likewise, by 2013 NOx will be down by 95% compared to the 1980s, while fuel consumption will have improved by as much as 40%.
Off-highway equipment has not been as strictly regulated as on-highway vehicles, but it is rapidly catching up.
There are two main regulating bodies for manufacturers to contend with, the Environmental Protection Agency (EPA) in the USA, and the EU for those operating in Europe. To make it more complicated the regulations are also split into engine power groups, with different dates for each power band.
From the start of this year, for example, machinery with engines producing more than 173hp (129kW) that is sold in North America or in Europe, has had to conform to the EPA’s Tier 4 Interim standard, which is much like the EU’s Stage IIIB regulation.
Doing it in stages
Tier 4 Interim and Stage IIIB call for a 90% reduction in PM compared to Tier 3/Stage IIIA, and a 50% drop in NOx. Tier 4 Final and EU Stage 4, which demand similar reductions again, will come into force in 2014. Engines with outputs of 100-174hp (75-130kW), will have to conform to Tier 4 Interim/Stage IIIB in 2012.
The first stage has been cleaning up the emissions that come from within the engine. Cleaner engine burn has been achieved through the use of increasingly complex electronic control systems, variable geometry and twin turbocharging, four valves per cylinder, more efficient air-to-air and air-to-water after-cooling, higher fuel injection pressures and the use of common rail injection systems.
Some improvements have been well received by customers, as they have also resulted in increased power and improved driveability, while reducing fuel consumption and exhaust emissions. But they have also increased complexity and cost, with all this additional technology adding to the purchase price of machines.
An opportunity for innovation
Most manufacturers have now passed the point where simply tuning what happens inside the engine is enough, and the after-treatment of exhaust emissions is becoming increasingly important. That said, JCB has managed to achieve the latest round of emissions regulations without resorting to after-treatment for its Dieselmax range of engines, though it admits that exhaust treatment will almost certainly be needed for Tier 4 Final/Stage 4.
“Meeting Tier 4 emissions legislation is a massive challenge but also a huge opportunity for innovation; an opportunity to come up with a solution that has real advantages for our customers,” says JCB director of engine programmes Alan Tolley. “Our strategy has been to meet Tier 4 interim emission standards without a DPF (diesel particulate filter), but also without any exhaust after-treatment.
“We have focused our research and development efforts on a high-efficiency combustion system. This approach also gives us very low fuel consumption levels, up to 10% lower than Tier 3,” he adds. “The real end user benefits come in the shape of reduced cost of ownership, reduced fuel consumption and even better reliability.”
“The real end user benefits come in the shape of reduced cost of ownership, reduced fuel consumption and even better reliability”
For those for whom after-treatment is necessary, this can be split into two areas, exhaust gas recirculation (EGR) and selective catalytic reduction (SCR), with manufacturers opting for one or both of the technologies. EGR, or cooled EGR in many cases, as the name suggests is the recirculation of a small percentage of the exhaust gas, which is fed back into the engine’s inlet valves and reburned.
SCR uses a catalyst within the exhaust silencer and an additive that in Europe is known as AdBlue, a 32.5% solution of urea in distilled water, which is injected into the catalyst to reduce NOx.
Diesel particulate filters are also being employed in the exhaust system to trap particulate matter and soot, regenerating themselves by burning off the trapped soot at regular intervals. This can be set to happen automatically or instigated by the operator.
This is one of the reasons why heat and, more importantly, heat dispersal, is becoming an increasingly important aspect of machine design. EGR raises in-cylinder temperatures, calling for larger engine radiators, while cooled EGR requires an additional cooler core alongside the engine’s radiator – the aftercooler for the turbocharged air – as well as an air conditioning condenser and extra hydraulic oil coolers.
A packaging problem
All of these cooling cores present both a packaging problem and an air-flow management concern. With a road-going truck the radiators are being pushed through the air on the front of the vehicle, contributing to the cooling effect. However, in an excavator or a dozer there is very little ram-air effect in what can be a fairly static machine.
To combat this, larger radiators are required, with bigger fans, which in themselves can sap energy from the engine and consume fuel. Exhaust heat management is also a consideration, as it is important to maintain temperatures all the way to the tailpipe for the after-treatment to function properly.
Most of the world’s engine manufacturers have been ready for the legislation for some time, many already supplying the on-highway market where the technology has been well proven.
Engine giant Cummins released new versions of its popular 300hp and 400hp engines in last September. Both use a DPF exhaust system and boast a 5% fuel efficiency increase. The firm’s smaller 70-160hp engines, due to be introduced in 2012, will use a new compact catalyst exhaust system.
While Cummins is one of the largest suppliers to machine manufacturers, plenty of equipment builders also have their own engine ranges. Caterpillar, for instance, has been developing its own engine range to meet legislation across the world for many years, while Case and New Holland will call upon sister company Fiat Power Train to supply the latest technology as required.
Operators on site will notice very little difference in their equipment, except perhaps slightly more power and hopefully improved fuel consumption. Those machines that rely on SCR after-treatment will need to have their AdBlue tanks refilled on a regular basis, but that can be checked when the machines are refueled.
Service intervals should be unchanged, although engineers will have to ensure that DPF regeneration is taking place to maintain low emissions.
One important consideration will be fuel quality. Tier 4 Interim/Stage IIIB engines must run on low sulphur diesel, or risk damage to the DPFs and to some fuel injection components. For a contractor working overseas, particularly in countries that don’t have low sulphur fuels of the qualityavailable in Western Europe, there may even be a requirement to take the fuel with the machines.
This will also have an effect on used equipment values, as it will make late model European and US specification machines less desirable in some parts of the world, where they have previously been well received. Given that it will not be possible to remove the technology that makes an engine conform with the legislation, overseas plant buyers will be looking closely to see what engines are installed in used machines.
Many on site will not be aware of the work that has gone into producing cleaner plant. It has, however, been a massively expensive business, and one that is not finished yet; as manufacturers look at the next stage of legislation and beyond.