Engines: Emissions and efficiency challenges

By Chris Sleight07 August 2008

Cummins unveiled the first of its interim Tier 4/Stage IIIB engines earlier this year. Unlike other

Cummins unveiled the first of its interim Tier 4/Stage IIIB engines earlier this year. Unlike other manufacturers, the company makes its own DPFs and other emissions control components, which it says

Where do you start with engines? The industry is working towards the most challenging emissions legislation it has ever faced, while at the same time trying to deliver better efficiency as well as accommodate greater quantities of biofuels - a controversial area in itself. Chris Sleight reports.

If you like a challenge, now would be a good time to get a job in the diesel engine industry. Having seen the current generation of Stage IIIA (European legislation)/ Tier 3 (US legislation) compliant machines onto the market over the last few years, thoughts are now turning to Stage IIIB/interim Tier 4 requirements, which come into force in 2011. Beyond that, the "final" Stage IV/Tier 4 laws will provide another challenge ahead of their 2014 implementation date.

At the moment these are the last pieces of legislation the industry will have to deal with, and it has been quite a journey, following the introduction of emissions restrictions for off-highway machines 1999 with Stage I/Tier 1. It does however remain to be seen whether this is truly the end of legislation for the industry.

In Europe there are signs to a move towards a different type of emissions measurement, with the European Commission and industry working in a Joint Research Council to investigate portable emissions measurement systems (PEMS). The idea is that rather than certify engines based on test cell results, it would be more effective to measure pollution in real-life situations.

It sounds deceptively simple, but such a device would have to tick a lot of boxes. It would have to measure and record emissions of various compounds including Carbon monoxide (CO), carbon dioxide (CO2) oxides of nitrogen (NOx) and volatile hydrocarbons in real time. The PEMS system would also have to measure and log other parameters including engine speed, torque and temperature, the vehicles position and ground speed and environmental considerations such as temperature, humidity and atmospheric pressure.

Ideally, all these capabilities would be put into a package that was small, lightweight and easy to install. It would also have to be robust enough to withstand the rigours of life on a construction site.

At the moment the European Commission's project is at a feasibility study stage, and the JRC is also working to finalise test protocols. By early 2010, the group could be in a position to start a number of pilot programmes with different manufacturers and different types of equipment.

Immediate challenges

If PEMS technology proves workable, it could mean big changes for engine and equipment manufacturers, but that is certainly some way off. In the meantime, the challenge of the forthcoming Stage IIIB/interim Tier 4 requirements is focusing minds ahead of the 2011 implementation date for 130 kW to 560 kW engines.

The challenge is an almost -90% reduction in particulate matter (PM). Engine manufacturers will use a range of technologies to achieve this, although at this stage many are talking in general terms, rather than launching specific engines.

According to Perkins' product marketing manager Allister Dennis, one change is that all engines will require turbochargers, and the company says it is looking at twin turbos for some models. As well as helping meet emissions requirements, these systems give the engine a greater power density and better transient response.

Cooled exhaust gas recirculation (EGR), like the use of turbo chargers, is a technology that helped deliver Stage IIIA/Tier 3 compliance, and meeting Stage IIIB/interim Tier 4 will see the EGR capacity of many engines increased to reduce NOx formation.

But the big new technology is diesel particulate filters (DPFs). These look like large cylindrical cans that are fitted into the exhaust system and contain a honeycomb like core that traps the solid PM particles.

Over time PM builds up in the filter, so the systems need a mechanism to burn off this soot to prevent the exhaust system getting blocked and ultimately destroying the engine. Some DPFs contain catalysts that burn the soot in normal operation, and this is generally termed ‘passive regeneration'. Other systems, or other applications require fuel to be injected into the filter to burn the soot - ‘active regeneration.'

High levels of sulphur in fuel can interfere with regeneration, so in order for the Stage IIIB/interim Tier 4 requirements to be met, the EU and US will be introducing ultra low sulphur fuels (10 to 50 parts per million of sulphur) for the off-highway market.

This will be a headache for equipment manufacturers that would like to produce a single model for all markets - it simply will not be possible. They will have to produce machines with a Stage IIIB/interim Tier 4 compliant engines for the EU and US markets, but will also have to make a variant for parts of the world where high sulphur fuel is used. As MR Dennis said, "OEMs need to understand fuel issues if they're building for export."

That's all very well for new machines, but what happens when a Stage IIIB/Tier 4 machine is sold by its European or US owner to a part of the world where high sulphur fuel is used? Without modification, there will be damage to the DPF and engine with potentially catastrophic results.

This is an issue that John Deere Power Systems has been thinking about. Product planning manager Doug Laudick told iC, "OEMs certainly need two platforms, but we're also looking at a ‘de-tier' kit for machines sold into other parts of the world."

According to Mr Laudick, this de-tiering would involve removing the DPF to replace it with a conventional exhaust, as well as some software changes to the engine's computerised management system. He added, "We would also need to have the possibility of ‘re-tiering' the engine at a later date."

Packaging

But putting these issues aside, the main problem facing equipment manufacturers today is fitting all these extra components into the engine compartment.

As Mr Dennis said, "The concerns are really all around packaging - the DPF & twin turbos add width and height."

These sentiments were echoed by Mr Laudick. "This may be the first time people are designing machines around the engine," he said.

For its part, John Deere will be basing its Stage IIIB/Tier 4 engines on its existing PowerTech Stage IIIA/Tier 3 models. Among the key technologies here is cooled EGR, high-pressure fuel injection systems and variable geometry turbo chargers (VGT).

With only three years to go until the introduction of Stage IIIB/interim Tier 4 laws for 130 kW to 560 kW engines, the issue of how manufacturers will fit these bulkier and more complex engines into their machines is becoming urgent. To date however, there are almost no such engines on the market.

The exception is Cummins, which launched its first next-stage engine at the ConExpo show held in Las Vegas in March, the 224 kW Tier 4 QSB6.7. Speaking at the launch of the engine, the company's president and COO, Joe Loughrey underlined the difficulty involved in meeting the new requirements.

"Tier 4 emissions may well be the biggest challenge the industry has faced. The requirements are equivalent to the two previous tiers combined, and the following 2014 requirements will result in virtually emissions free engines," he said.

Cooled EGR and high-pressure common rail fuel injection systems help reduce the formation of NOx in the QSB6.7 by lowering the combustion temperature. The exhaust features Cummins' own Particulate Filter, and this is something the company puts a strong emphasis on.

Unlike other engine manufacturers, Cummins does not buy-in add-ons like DPFs, but builds them itself. This, it says, helps ensure they are more suited to the application. Susan Harrison, executive director of Cummins Industrial Engineering said, "The Cummins Particulate Filter for Tier 4 is an exceptionally rugged design which is hardened to withstand severe shock loads and vibration."

She continued, "A compact profile with flexible inlet and outlet orientations enable the Cummins Particulate Filter to integrate more effectively with varying types of equipment installations. Together with the Cummins Direct Flow air filtration system, the Particulate Filter aftertreatment combines the packaging integration for a complete air-in to exhaust-out installation for Tier 4 applications."

Another point that Cummins is keen to stress is that although its new engines will be more complex, this won't be at the expense of reliability. The company says it will complete 100000 hours of test cell work and 50000 hours of field-testing on the new engines in the run-up to 2011.

"I challenge you to find a more dependable engine in the market today," said Mr Loughrey. He added that engines like the new QSB6.7 would, "...offer mature levels of reliability at introduction."

Another interesting, and increasingly important point is that Cummins has found some savings in fuel efficiency with its new engines, as has Perkins

Hybrids

With oil prices going through the roof this year, fuel efficiency is of course a major issue. One of the solutions is the use of hybrid drive systems, where electric motors are added to the powertrain alongside traditional diesel engines. The electric motor is used at low revs, where diesel engines are inefficient and provide little torque.

At higher revs diesels work more comfortably and can charge batteries for the electrical system as well as drive the machine. There are also systems that capture the energy used in braking to charge the electrical system - harnessing more ‘free' energy that would otherwise go to waste.

These systems are expensive compared to traditional diesel-only powertrains, but persistently high fuel prices have made them economically viable. This year's ConExpo show saw Volvo unveil a prototype ‘mild' hybrid wheeled loader, which is due for a commercial release next year. The ‘mild' means that although there is an electrical system on board, it is not powerful enough to run the machine on its own during normal operation.

Komatsu has got ahead of the game though, with the commercial launch of a hybrid 20 tonne excavator on the Japanese market in June. This uses capacitors rather than a battery to store electrical energy and the company says it burns -25% less fuel on average than a standard PC200.

Manufacturers that don't have the resources of Volvo and Komatsu to develop hybrids on their own will doubtless be interested in the latest news from Deutz. The company has announced the development of a mild hybrid package comprising a four-cylinder diesel engine, electric motor, battery and control unit that it says could reduce fuel consumption by -30%.

Deutz developed the hybrid drive in conjunction with engine control system specialist Heinzmann. The electrical system is rated at a nominal 15 kW output, with a peak capacity of up to 30 kW, almost doubling the power of the diesel engine.

A prototype unit has already been fitted to an Atlas Weyhausen AR65 wheel loader. While the standard loader is powered by a 68 hp (51 kW) Deutz TCD 2011 diesel engine, the hybrid version has been replaced by a smaller 50 hp (37 kW) D 2011 non-turbo-charged oil cooled version.

Deutz says the earliest the hybrid unit is likely to go into series production is 2010.

Another interesting area is diesel-electric drives. This technology has been popular in large mining trucks for many years, and involves using the diesel engine as a generator to drive electric motors rather than a mechanical transmission. This helps eliminate some of the losses associated with mechanical drives and also offers more design flexibility, because electrical cables are easy to route than drive shafts.

An interesting example of this is Caterpillar's D7E dozer, again launched at ConExpo, which the company says moves +25% more material per litre of fuel than a traditional D7. Another bonus is that the machine has -60% fewer moving parts than a conventional dozer, so should be more reliable.

Caterpillar clearly sees more potential for this technology as group president Doug Oberhelman explained "You can certainly expect to see that technology expand over the next few years and that will certainly manifest itself in other machines," he said.

The next Cat machines to get a diesel-electric makeover will be some of its mining truck range, with new models expected to be on display at September's MinExpo show in Las Vegas.

Biofuels

Finally, and perhaps most controversially is the issue of biofuels. A few years ago these looked like the answer - or at least part of the answer to dwindling oil reserves and rising fuel prices. The idea was to grow sugar crops such as sugar beet and sugar cane and starchy plants like corn and maize to produce ethanol by fermentation, or to grow oily crops like soybeans and rapeseed to provide a diesel-like fuel oil.

As a result, many manufacturers now rate their engines to accept a certain proportion of biodiesel. Most will accept fuels that are 5% biodiesel (B5) and many will go further. John Deere for example says fuels up to B20 can be used with all of its Stage IIA/Tier 3 engines, while Perkins' Mr Dennis says the company's aim is to certify all of its engines up to B100.

The reason for this apparent caution is that biodiesel is not a like-for-like substitute for petroleum diesel. With repeated exposure biodiesel can damage seals and gaskets and it can also degrade crankcase oils. It can also degrade, especially if stored incorrectly, and delivers slightly different performance than petroleum diesel.

It is therefore important that machine owners don't use biodiesel in an engine that is not certified for it, and don't exceed the specified proportion of biodiesel. This could damage the engine and while invalidating the warranty at the same time - an expensive mistake!

However, just as the industry is adapting to this legislative change, the rationale behind biofuels is coming into question. One problem seems to be that land previously used for food crops is being turned over to cultivate bio fuel crops, which has contributed to the global spike in food prices. Another concern is that forested areas have been cut down to plant bio fuel crops, which is hardly a positive environmental step!

Even without these problems, biofuels are not carbon neutral, because they require machines and chemicals to cultivate, which means extra energy and extra co2 in the atmosphere.

It is a controversial argument, and one that engine manufacturers are quite wisely steering clear of, preferring to fall into line behind government policies. As Mr Oberhelman said, "Our goal immediately is to use all the biomasses available today, but the issue of biofuels is a huge issue for society."

Future

Whether biodiesel becomes a fuel of the future remains to be seen, but as long as oil prices stay high, there are likely to be more hybrid drive systems developed and fitted into construction machines. All this while the industry grapples with ever more stringent emissions requirements. It'll be a challenge!

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