Tier 4 Final engine technology

Manufacturers of off-highway diesel engines are competing to come up with the most efficient ways of reducing exhaust emissions in line with new laws that come into force in the EU, Japan and the US from 2014.

The broadly equivalent European Stage IV, Japanese Tier 4 B and US Tier 4 Final laws will see another reduction in nitrous oxide (NOx) on top of the cut in particulate matter (PM) which was achieved under the current legislation. The 2014 laws will see PM and NOx emissions reduced to similar levels to the ambient atmosphere, so essentially there will be zero pollution.

For the EU and US, engines rated between 130 kW and 560 kW will be affected in 2014, and the 75 kW and 130 kW power band will have to comply from 2015. Japan’s Tier 4 B starts to take effect in 2015.

Meeting these stringent requirements means diesel engines may incorporate a huge range of systems, from electronic engine management to high pressure injection and various forms of exhaust gas aftertreatment.

These include cooled exhaust gas recirculation (EGR), selective catalytic reduction (SCR), diesel oxidation catalysts (DOC) and diesel particulate filters (DPF) – and manufacturers are mixing and matching technologies to achieve compliance.

Day-to-day impact

But the real question for users of construction equipment is what impact these new engines will have on their day-to-day lives on-site. The regulatory challenges are the same for everyone, but manufacturers are in fierce competition to come up with the best combination of technologies to meet them.

Aftertreatment components like SCR, DOCs and DPFs tend to add bulk to the engine compartment, which means redesigning these spaces and potentially affecting visibility for the operator.

In addition, SCR requires the use of a urea-based diesel exhaust fluid (DEF) such as AdBlue, which contractors must keep topping up every four or five refuelling stops. There could also be extra servicing implications for cleaning or replacing DPFs, and aftertreatment systems also require more expensive low-ash oils to be used in the engine.

In August, Volvo CE became the latest manufacturer to reveal its Tier 4 Final/Stage IV technology – the result of a four year development programme, which makes use of EGR, along with SCR and a DPF as aftertreatment.

Due to be introduced next year, the new engines have undergone bench and field testing under which fuel efficiency increases of +5% and a reduction in CO2 emissions of -5% have been recorded over their Stage IIIB equivalents.

This testing programme involved more than 25,000 running hours in articulated haulers, wheeled loaders and excavators in a range of environmental conditions, from sub-zero temperatures to extreme heat and at high altitude.

Volvo selected SCR as the technology of choice to meet the regulations since it allowed the development of the new engine without having to dramatically change the basic design.

Volvo will be using six Tier 4 Final/Stage IV engines – the 80-116 kW D4, the 100-180 kW D6, the 160-250 kW D8, the 235-265 kW D11, the 220-329 kW D13 and the 350 kW D16.

Meanwhile, other manufacturers are finding ways of avoiding the use of components such as DPFs on some models, cutting out the cost and service implications of this component altogether.

John Deere, for instance, now offers a line-up of EU Stage IV/US Tier 4 Final engines covering the 36 kW to 448 kW band. For engines rated 130 kW and above, the Stage IV/Tier 4 Final engines use EGR and a DPF, along with a DOC and an SCR system, but the manufacturer achieved compliance for its 63 kW to 104 kW PowerTech PWL 4.5L engines without using a DPF.

The PowerTech PWL 4.5L is equipped with an Integrated Emissions Control system consisting of SCR, a DOC and EGR technology. John Deere said optimising the combustion process and improving the conversion efficiency of the SCR were what enabled it to do without a DPF.

John Piasecki, director of marketing, sales and customer support for John Deere Power Systems, said, “We believe the elimination of the DPF will serve OEMs and end users well in the very competitive 56 kW to 104 kW segment, balancing packaging and product cost considerations with performance and operating cost requirements.”

Reducing aftertreatment

For its part, Liebherr also aimed to use as little aftertreatment as possible with its Stage IV/Final Tier 4 engines. At the moment, Liebherr supplies 11 different basic engines in the power categories from 130 kW to 750 kW. The 4- and 6-cylinder inline engines, the V8 and V12 all comply with the exhaust emission limits that will apply from 2014.

To keep the system simple and optimise exhaust emission control, the company opted to focus on SCR technology only. It claimed this approach had economic benefits for the customer and also simplified construction machinery design.

With the aim of reducing particulates formed inside the engines, Liebherr examined the entire combustion process. Among other parameters, the injection pressure and compression were increased and internal friction reduced.

Meanwhile, Caterpillar’s Stage IV/Tier 4 Final engines span
25.2 kW to 895 kW, and are available with a range of aftertreatment technologies including EGR, DOC, DPF and SCR – depending on the power band and application. In addition, a DPF-free package is available on some platforms.

Mike Reinhart, Caterpillar industrial marketing manager, said, “As we designed our Stage IV and Tier 4 Final engines, we did so with the end in mind in order to make integration as simple as possible for our OEM customers.”

Flexibility

Sister company Perkins has also tried to be as flexible as possible. Its Stage IV/Tier 4 Final line-up of engines up to 225 kW is also designed to minimise the impact of aftertreatment. The 1200 Series models, for instance, feature a DPF that is packaged together with the DOC canister and the SCR system into one integrated module that can be positioned remotely in a machine chassis or directly on top of the engine.

The manufacturer’s goal is to minimise installation work for OEMs. For instance, the DPF uses passive regeneration to burn away the soot in the DPF – a process which does not require the operator to be involved with and as such facilitates easier installation in the engine bay since no direct access is required for ash removal.

Perkins said its Technology Integration Workshop programme has so far overseen more than 500 engine installation projects for more than 150 global OEMs. It has recorded total fluid consumption improvements of up to 9% over the gains made at the Stage IIIB/Tier 4 Interim phase.

Cummins, meanwhile, has introduced two new Stage IV/Tier 4 Final engines this year – the 250 kW to 382 kW QSM12 and the 63 kW to 98 kW QSF3.8. Designed for wheeled loaders, excavators and cranes, the larger QSM12 uses SCR and a DPF to comply with next year’s laws, but without the use of EGR.

The company has also been testing its Stage IV/Tier 4 Final range, clocking up over 75,000 machine hours so far in North America and Europe. The engines have been put to work in a variety of tough environments from the high altitudes of the Alps and the hot and humid weather of Florida, to running in the dry heat of Texas.

Cummins said nearly 70 engine models had been tested so far in everything from wheeled loaders, and material handlers to rock drills and air compressors.

The company said the engines were performing well, with more uptime hours recorded than originally planned across the complete 2.8 to 15 litre product range. Fuel consumption levels see a 7% to 8 % improvement over Tier 3 machines with low levels of DEF consumption, according to the company.

Jeremy Harsin, service and new product introduction team leader at Cummins said it was the most extensive and varied field test that the company had ever undertaken. “From our results we are fully confident we have a dependable and proven Tier 4 Final solution,” he added.

Deutz, meanwhile, opted for an ultra-compact design in its latest Stage IV/US Tier 4 Final engine launch, which comes in the form of the TCD 2.9 L4. This unit covers a performance range of between 30 kW and 55.4 kW.

Deutz claimed to have enabled drop-in installation of the entire system. This is because the TCD 2.9 L4 is fitted with a modular exhaust gas aftertreatment system which can optionally be fitted to the engine.

Also in the lower output ranges, Hatz has released a Stage IIIB/US Tier 4 Final-compliant engine – ­the 4H50TIC, which has an output of 55 kW. The 4H50TIC meets the emissions laws without a DPF, saving on space, money and servicing. Cooled EGR technology and a DOC are used to reduce emissions.

Managing director Wolfram Hatz said the 4H50TIC consumed diesel at a rate of 210 g/kWh – a figure which he said was around -10% lower than competitor models.

“This fuel consumption figure includes the cooling fan and alternator, and we really believe it represents a strong advantage to customers,” Mr Hatz said.

But with the prospect of a further stage of EU Stage V laws currently being debated, manufacturers are likely to continue to focus on flexible ways to reduce diesel exhaust emissions further beyond 2014. Ulrich Beutke, who co-ordinates advisory body and industry association work at Tognum/MTU, said engines rated under 560 kW would very probably have to meet even stricter emission limits in future.

“Although we don’t know any figures yet, all the signs are that the EU will base Stage V on the Euro 6 emission limits for commercial vehicles,” Mr Beutke said. As well as potentially reducing NOx and PM emissions to 0.4 g and 0.01 g per kWh respectively, there could be a new, as yet unknown particulate number (PN) limit.

This means the soot particulates would no longer simply have to be within a specific weight limit, but also below a specified number, according to Matthias Vesper, who also monitors the work of environmental standards committees for Tognum/MTU.

This is because the health hazards associated with PM are linked to smaller particles, which may escape through current DPF systems. Targeting a lower PN limit is a way to reduce emissions of these more harmful specks.

However, this next phase of legislation is not likely to come into force before 2019 according to Mr Vesper.