Manufacturers of engines for construction equipment are extremely busy at the moment, with their hands full not only supplying the latest, low-emissions engines that comply with the current EU Stage IIIB (US Tier 4 Interim) emissions laws, but also developing and testing engines that comply with the next wave of legislation that comes into force in 2014 - EU Stage V and US Tier 4 Final.
Meeting these stringent requirements mean diesel engines incorporate a huge range of systems, from electronic engine management, to high pressure injection, exhaust gas recirculation and various forms of exhaust gas aftertreatment.
In one sense the end is in sight with the 2014 laws, which will see pollution levels reduced to around the ambient levels seen in many cities.
But it has to be wondered whether that will really be the end of it. While diesel is arguably the most power-dense, efficient method of providing the energy to run construction equipment - with easily portable and widely available fuel - the price of oil is rising, and this is a factor which increases the pressure on manufacturers to reduce consumption, or find alternatives.
In addition, regulators are not known to sit still for long - news of EU Stage V laws is expected soon, for instance. In this respect, there are several potential areas of focus for regulators. One is the problem of particulate matter (PM) - the black soot typically associated with diesel engines.
The current and upcoming emissions laws focus on reducing PM emissions using exhaust filters to near-zero levels, but one of the upshots of this is the fact that what little PM does still escape is likely to be far smaller, and paradoxically more harmful to humans. This is because these ultra-fine PM emissions are more likely to be absorbed into the bloodstream if they are inhaled.
A spokesperson from a major engine manufacturer who wished to remain anonymous said his company was already looking into the development of new filters and regeneration processes in anticipation of even stricter legislation that will aim at stopping the release of ultra-fine PM into the environment.
Focus on Co2
Another potential focus for the next wave of regulations is CO2 emissions, according to the president of diesel engine manufacturer Perkins, Gwenne Henricks, who is also a vice president of its parent company Caterpillar, with responsibility for industrial power systems and growth markets.
"I think there will be something around CO2 reduction, which means essentially burn less fuel or burn fuel that has lower CO2 properties in the emissions," she said. "If it's burn less fuel, there'll be efficiency improvements that we'll want to make.
"The big key there is that we will continue to develop more and more efficient engines. You certainly see the trend of increasing in power density - you'd like to get more efficiency out of a smaller package and burn less fuel to get the job done."
She added, "As an engine manufacturer, we'd like to do that, but I think there's a bigger prize in matching the engine well to the drive train and hydraulics, and then there are hybrids and energy storage of one form or another."
She said there was also a prize at total machine level and then again at optimising the machines and the job site.
"So it's about efficiency - burning less fuel, but then it's about collaboration between engine manufacturers and machine manufacturers, right through to the customers."
If law makers were to target CO2 emissions there are two ways they could do it. One would be to put higher taxes on fuel, so manufacturers could get a commercial advantage by making machines that were more fuel efficient. A different approach would be to regulate machines or engines in the same way the current emission laws do, and give manufacturers a target they must achieve to be able to market their products.
"My best guess is that we'll see both," said Ms Henricks. "It will depend on the different social and political considerations in different regions of the world. It would be nice to get a harmonised approach, but I wouldn't bet on it."
Another more current area of interest is in the use of natural gas as a fuel for construction equipment, particularly following the discovery of large deposits of shale gas in North America, northern Europe and South America from the late 1990s onwards.
Caterpillar has announced plans to develop, in partnership with fuel specialist Westport, natural gas-powered engines for construction equipment.
Steve Fisher, vice president of Caterpillar's large power systems division, said many of Caterpillar's customers were asking for natural gas-powered equipment in order to reap the financial and environmental benefits.
"The programme positions Caterpillar to offer the broadest product line of natural gas-fuelled machines and equipment, and capitalise on the attractiveness of natural gas as an alternative mobile fuel," he said.
Westport supplies clean-burning fuel technology for engines, including compressed natural gas (CNG), liquefied natural gas (LNG), hydrogen, and renewable natural gas (RNG) fuels such as landfill gas. It has also developed High Pressure Direct Injection (HPDI) technology for the fuels.
Caterpillar said the two companies would combine technologies and expertise to become the first in the market to offer a Westport natural gas HPDI fuel system for high horsepower, off-road machines.
Caterpillar will fund the development programme, initially focusing on mining trucks and locomotives, and Westport will supply key components. Commercial production is expected to begin in about five years.
David Demers, CEO of Westport Innovations, said the agreement was an opportunity for 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 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.
Alternative fuel sources
Meanwhile, Deutz is also focusing on developing technology for alternative fuel sources. In May, the company released its first Stage IIIB-compliant engines which run on biodiesel. Developed with the agricultural market in mind, the TCD 6.1 L6 and TCD 7.8 L6 models run on 100% EN 14214 biodiesel and feature a 2,000bar injection system as well as selective catalytic reduction (SCR) aftertreatment.
Fuels from renewable, sustainably produced bio-resources such as rape seed oil enable a virtually 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 largely compensated for.
Deutz said it had conducted extensive 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 currently 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.
The last few years have seen the launch of a handful of hybrids in the industry, for instance, as well as diesel electric technology - using the diesel engine as an on-board generator to drive electric motors - which has been around for decades.
And the market is already seeing the introduction of innovative machines which use some energy reclamation technology to complement engine performance - Liebherr's LH80M Litronic material handler, for instance, which was unveiled at Intermat. As well as being powered by a 230kW Liebherr Stage IIIB/Tier 4 Interim engine, this machine also contains an energy recovery cylinder (ERC) - a third hoist cylinder mounted between the two hoist cylinders and filled with nitrogen gas.
By compressing the nitrogen, the ERC system stores the energy released as the working equipment is lowered. During the next lifting movement, the nitrogen expands and the stored energy is added to the power exerted by the hoist cylinders. Liebherr claims up to 80kW of additional energy is contributed by the energy recovery cylinder, meaning less power is needed from the diesel engine, and so its fuel consumption is reduced.
However, each approach - including electrical solutions such as batteries - has application-specific benefits and drawbacks, and Perkins' Gwenne Henricks claimed that this meant that it was unlikely there would be a one-size-fits-all solution.
"That's why I come back to saying I foresee diesel or gas engines, in combination with other technologies, having a role for a long time to come," she said.