Alternative power for engines

Legislation on diesel engine exhaust emissions in the off-highway sector will take another step in 2014 when the European Stage IV and US Tier 4 Final laws start to come into force for new equipment. This will see another reduction in nitrous oxide (NOx) on top of the cut in particulate matter (PM), which was achieved under Stage IIIB/Interim Tier 4.

On top of that, discussions are under way in Europe for a further Stage V of regulations, which is likely to have several strands to it. First, it is expected to address diesel engine sizes that are not currently covered by the regulations, which is to say below 19 kW and above 560 kW. Second, engines from 19 kW from 37 kW, which were affected by regulations up to and including Stage IIIA but not the latter ones, are likely to see more legislation.

Stage V is also expected to include legislation on spark ignition (petrol) engines as well as diesel engines in constant speed and stationary applications, such as generators.

Diesel alternatives

But as engines get more complex with the extra systems required to cut emissions, they also get more costly. This has certainly been the case with Stage IIIB/Interim Tier 4, where most engine manufacturers have added bulky and expensive aftertreatment in the exhaust systems to achieve the required reductions.

This has spurred the industry in a number of directions. First, manufacturers are looking at ways of making their engines more efficient and more powerful, so that the increase in purchase costs can be partially offset for the customer by increased productivity and lower fuel bills.

Second, the regulations have made other expensive fuel saving technologies, such as advanced transmissions, diesel electric and hybrid systems more viable. These can lead to efficiency gains in operation that can offset the higher purchase costs, and in the case of hybrids, they can also mean that a smaller, cheaper engine can be used.

There is also interesting talk around machines that have traditionally been powered by engines around 50 kW - 8 tonne excavators, small backhoe loaders, skid steer loaders, compact wheeled loaders, 6 tonne rollers etc. - as there may be scope to use a 37 kW or less engine as part of a hybrid system that would take the total power up to 50 kW.

The advantage here is that these sizes of diesel engines are only subject to Stage IIIA laws at the moment, so the extra expense of aftertreatment would be avoided. However, the costs of a more complex hybrid system might be difficult to offset in such competitive parts of the equipment industry and on small machines, where the engine is a significant part of the total cost. And with Stage V looking like it will apply to these smaller engines, this idea of 'ducking' the legislation would only have a short life anyway.

Another barrier to this approach is the fact that it would only work in Europe. In the US, next year will see a requirement for a -90% reduction in PM for 19 kW to 56 kW engines.

A different approach would be to move away from diesel engines and their expensive regulations and look at other fuels.
Caterpillar has announced plans to develop, in partnership with fuel specialist Westport, natural gas-powered engines for construction equipment - an area that has grown in importance following the discovery of major shale gas deposits, including in the US, from the 1990s onwards.

Westport supplies technology for engines powered by compressed natural gas (CNG), liquefied natural gas (LNG), hydrogen, and renewable natural gas (RNG) fuels such as landfill gas. David Demers, CEO of Westport Innovations, said the agreement represented an opportunity to transform the off-highway equipment industry.

"The substantial price difference between natural gas and diesel fuel is resulting in a strong financial incentive to enable off-road applications to take advantage of low natural gas energy costs without sacrificing operational performance," he said.

"There is also a clear environmental incentive because of the reduced carbon emissions. Adding to the solid business case for this programme is the potential to convert existing field units to natural gas - opening up a whole new market opportunity," Mr Demers added.

Meanwhile, Deutz is also focusing on developing technology for alternative fuel sources. In May, the company released its first Stage IIIB-compliant engines to run on 100% biodiesel.

Developed with the agricultural market in mind, the TCD 6.1 L6 and TCD 7.8 L6 models feature a 2000 bar injection system as well as selective catalytic reduction (SCR) aftertreatment.

Fuels from renewable, sustainably produced bio-resources such as rape seed oil enable a relatively closed CO2 cycle because the plants from which the biofuel is produced take CO2 out of the air during growth. This means that the CO2 emissions from the biofuels combusted in the engine are partly compensated for.

However, there are still CO2 emissions associated with processes like fertilising, harvesting, processing and transporting the biofuel.

Deutz has conducted field tests to validate the suitability of biodiesel as a fuel. A company spokesperson confirmed that while the Stage IIIB TCD 6.1 L6 and TCD 7.8 L6 engines have been designed for the agricultural market, Deutz was also considering the development of a biodiesel engine for the construction market.
While natural gas and biodiesel engines appear to be on the cards for the off-highway equipment of the future, there are a variety of other technologies also under development.

Latest diesels

But these innovations will of course take time to come to the market. In the meantime, there is still a strong focus on diesel engines, and in particular the new models that are being released to reach the requirements of Tier 4 Final and Stage IV.

The main change from Interim Tier 4/Stage IIIB to Tier 4 Final/Stage IV is the addition of selective catalytic reduction (SCR) exhaust aftertreatment systems to bring down NOx levels. These complement existing exhaust gas recirculation (EGR) systems, which reduce NOx in the combustion chambers themselves, along with diesel particulate filters (DPFs) and diesel oxidation catalysts (DOCs), which remove PM from exhaust gasses.

Caterpillar for example has developed what it calls a Clean Emissions Module (CEM) for the Tier 4 Final challenge. The unit includes the DOC, DPF and SCR modules and it was shown to the public for the first time at this year's Intermat exhibition on a C7.1 Acert industrial engine and the C13 Acert industrial power unit.
The C7.1 is a 7 litre, 6 cylinder engine with an output from 116 to 225 kW and a peak torque of 1208 Nm.

The space requirements involved with installing the engine in a final machine are a key concern for equipment manufacturers, and Caterpillar says it has designed the C7.1 to allow ease of installation. The CEM is an integral component and can be mounted in a variety of locations, depending on the application. It can also be supplied from the factory installed as a module with the engine or packaged remotely within the chassis or above the engine.

The C13 Industrial Power Unit takes this a step further, as the 287 to 388 kW unit is supplied as a complete package, including the radiator, flywheel, alternator, aftertreatment module, pre-assembled wiring harness, advanced electronics and configurable software.

Caterpillar industrial power systems marketing manager Mike Reinhart said, "The goal is to ease the transition from Tier 4 Interim/Stage IIIB to Tier 4 Final/Stage IV. The C13 Acert power unit maintains the same design footprint and claims no additional space requirements compared to the Tier 4 Interim/Stage IIIB product."

John Deere Power Systems used Intermat to unveil its Power Tech PSS 9.0L Tier 4 Final/Stage IV engine. Like Caterpillar, the company has designed an all-in-one aftertreatment package to meet the new legislation, which it describes as its Integrated Emissions Control, containing the DOC, DPF and SCR.

"We're committed to using the right combination of technology building blocks to meet increasingly stringent emissions regulations and customer expectations," said John Piasecki, director of worldwide marketing, sales and customer support for John Deere Power Systems.

"This building-block approach led to the Integrated Emissions Control system and an optimised Final Tier 4/Stage IV technology solution that we're confident will deliver emissions compliance without sacrificing power, performance, ease of operation, fluid efficiency, reliability, durability or economical operating cost," he added.

An interesting manufacturer to watch for Stage IV/Tier 4 Final engines will be JCB. Earlier this year it unveiled the Stage IIIB/ Interim Tier 4 version of its 55 to 129 kW Ecomax engine, which is unique in the market for achieving compliance with legislation without the use of any aftertreatment.

Although it seems unlikely this will be possible for the more demanding Stage IV/Tier 4 Final legislation, the company claims a significant competitive advantage with its current generation of diesel engines, which are fitted in machines such as its backhoe loaders, telescopic handlers, skid steer loaders and some models of excavator and wheeled loader. It says running costs will be lower than competitors because there is no DPF requiring periodic servicing and no need for the diesel exhaust fluid (DEF) that is required in SCR systems.

"We at JCB are proud that through engineering excellence and innovation, we have been able to achieve the power and torque that our customers require to get the job done, while lowering fuel consumption and meeting stringent emissions criteria from around the world," said Alan Tolley, JCB's director of engine programmes.

The importance of performance in these technically demanding times means engine manufacturers with a competitive advantage can win new business. Tognum subsidiary MTU for example announced earlier this year that it has won a new contract to supply its 400 and 500 series engines to Bomag for use in its landfill compactors.

The industrial diesels are derived from Tognum's OM 460 LA and OM 502 LA Mercedes-Benz on-highway engines, a market which is further ahead of the construction equipment industry in terms of emissions compliance. This meant MTU could not only supply engines to meet the current Stage IIIB/Interim Tier 4 laws, but also prototypes for the Stage IV and Tier 4 Final legislation.

In terms of performance, MTU said its engines' ability to deliver high power and torque were key factors that allowed the compactors to operate on steep inclines, move piles of waste and manoeuvre quickly.

At the lighter end of the engine spectrum, Yanmar announced earlier this year that it had achieved Tier 4 certification from the US Environmental Protection Agency (EPA) for it 4TNV88C, a 35.5 kW 2.2 litre engine. Yanmar also claims it is the world's first engine to be certified to this level by the California Air Resources Board (CARB).

Yanmar has achieved emissions compliance in a similar way to manufacturers of larger engines, with electronic control, high pressure fuel injection, EGR and a DPF. The company says these technologies have allowed it to achieve the requisite -90% reduction in NOx emissions.

Similarly, Kohler has secured Tier 4 Final approval for its 1.9 litre and 2.5 litre engines in the US, but without using a DPF. The company has instead opted for a combination of direct fuel injection, EGR and a DOC.

It went on to say that based on 1,000 hours per year usage and prevailing prices in the US, the engines offered US$ 1,400 annual savings on fuel and US$ 116 per year on oil, compared to units with indirect injection and a DPF.

"The power and torque of these engines in relation to their compact sizes and reduced fuel consumption have clear advantages to construction, industrial and agricultural equipment manufactures and end-users," said Dick Fotsch, president of Kohler's global power group.

Kohler also markets engines under the Lombardini brand.

Competitive edge

While alternative engine designs and power sources are under discussion, the construction equipment market remains firmly wed to the diesel engine for the time being. That means there are opportunities for manufacturers to differentiate themselves with alternative technical solutions to emissions control, and with designs that offer better fuel efficiency and other operational savings.