New stage technologies

The Key Requirement of the Stage IIIA exhaust emissions laws is a reduction in the levels of hydrocarbons (HC) and oxides of nitrogen (NOx) emitted by the diesel engines used in non-road mobile machinery, which includes most types of off-highway construction equipment.

The first point to note is that while previous laws have dealt with HC and NOx emissions separately, Stage IIIA is drawn up in terms of a combined value for the two pollutants. As far as 130 to 560 kW engines are concerned, the first powerband to be affected by the laws at the start of this year, combined HC and NOx may not now exceed 4 g/kWh. The previous limits under Stage II, which came into force for this powerband at the start of 2002, was for 1,3 g/kWh of HC and 6 g/kWh of NOx. So although it is not exactly comparing like with like, the Stage IIIA requires a -55% reduction in these pollutants.

NOx and HC are not the only pollutants that concern the European Commission. The laws also specify maximum levels of carbon monoxide (CO) and particulate (PM) pollutants – the black soot that is often associated with diesel engines. However, CO limits remain largely unchanged from Stage II to Stage IIIA.

PM levels, which present a different technical challenge to gaseous pollutants, also remain unchanged in this phase of the laws. They will however be the main focus of the Stage IIIB legislation, which comes into force in 2011.

Beyond that, a fourth Stage is planned for 2014, which will require a further reduction in NOx emissions. Rather confusingly, Stage IIIB and IV will deal with NOx and HC as separate pollutants once again. Stage IV will demand just 0,4 g/kWh of NOx and 0,19 g/kWh of HC.

Comparing this back to the first phase of this legislation, which started with Stage I in 1999, NOx emissions will have come down from 9,2 to 0,4 g/kWh – less than 5% of the original permissible levels. Indeed, such concentrations of NOx are on a par with the atmosphere in a major city. As one equipment manufacturer famously quipped, the purpose of Europe's emission laws seems to be to make diesel engines into air purification systems!

Technology

So how are manufacturers achieving compliance with the new regulations?

The answer is that there are a range of systems and technologies that can contribute to reductions in NOx emissions. While there are some common ones across the industry, there are also some significant variations, so no two manufacturers' solutions are exactly alike.

To start with the common elements, almost all Stage IIIA-compliant engines now feature an electronic control unit. Prior to the development and prototyping of these engines, it was assumed that a computerised engine control unit (ECU) would be an absolute 'must' to achieve compliance. This is generally the case, although it should be added that some models of Perkins' Stage IIIA-compliant 1100 D range are available with mechanical control.

Computerised engine management is not just there to reduce emissions, although this is the primary reason. These modern engine management systems also help to optimise fuel consumption. They can also be used to monitor numerous aspects of the engine's performance and operating parameters, and raise the alarm if there is a problem such as overheating or low oil pressure.

Another common feature of Stage IIIA engines is high pressure fuel injection, often using a low noise 'common rail' system, which is controlled by the ECU. These systems allow very precise management of each combustion cycle, often by injecting the fuel in several 'squirts', to ensure it is fully burnt without reaching excessive temperatures.

The common rail concept is a patented system that was developed by Fiat in the 1990s and subsequently sold to Bosch. While some engine manufacturers pay to use this technology, others such as Deutz, DaimlerChrysler and Hatz have developed their own high pressure injection systems.

Exhaust Gas Recirculation (EGR) is another common technology, although several manufacturers, most notably Caterpillar, have not gone down this route. As the name suggests, EGR systems cool a proportion of the exhaust gases and then channel them back into the combustion chamber, which helps reduce the combustion temperature.

Temperature is important, because the higher it gets, the more atmospheric nitrogen is 'fixed' to produce NOx. This also explains why several manufacturers incorporate systems that cool the charge air before feeding it into the combustion chambers.

So how are manufacturers applying the technology? Volvo's new solution is V-ACT, which features air-to-air intercooling, with some larger units sporting four valves per cylinder and overhead camshafts. Volvo says the keys to the design are the high pressure fuel injectors and the engine management system (EMS) that controls them.

Cummins is another that has gone the common rail route with its Quantum range of engines, and charge air cooling is another feature that it has applied to some engines in the range. In common with other manufacturers, much effort has been expended by the company on developing a highly efficient electronic engine management system, a feature it believes is crucial in meeting the legislative requirements.

Scania's engines use electronic management along with a combination of EGR and common rail fuel injection. The company expects to use Selective Catalytic Reduction (SCR) technologies to reduce emissions further in the future.

John Deere's Tier 3/Stage IIIA PowerTech Plus engine range makes use of both common rail high pressure fuel injection and cooled EGR, with a variable geometry turbocharger to help drive the EGR system. As usual, an ECU is at the heart of the engine, controlling the air-to-fuel ratio, multiple fuel injections and the amount of EGR, while at the same time providing diagnostic functions.

Deutz, meanwhile had developed its own version of the Common Rail injection system for its latest generation engines in the form of a twin pump design that will leave the basic engines unchanged. Called the Deutz Common Rail (DCR), this design will be introduced across the full range of Deutz diesels over time.

DaimlerChrysler's Detroit Diesel and Mercedes Benz engines feature turbo charging with charge air cooling. Once again, a high pressure fuel injection system is used, a variation on the common rail theme, which uses a ring fuel circuit with solenoid operated injectors. This, the company claims, provides even lower emissions than standard common rail packages. Naturally, an electronic engine management system is used to control engine performance.

Caterpillar has developed its own system, ACERT, which is an advanced package that is built around the concept of controlling the combustion process to minimise emissions. Combustion chamber and cylinder head design have been optimised to improve combustion efficiency, and a Mechanically Actuated Electronically Controlled Unit Injection system provides multiple injection and rate shaping capability. This is a proprietary system that does not make use of the common rail concept.

Hatz has also gone a different route for its new 2, 3, and 4 cylinder W35 engine family, which is also available in two turbocharged versions, the 3 and 4 cylinder W35Ts. It covers a power range from 5,2 to 36,5 kW up to a maximum speed of 3600 rpm. The major difference is the way Hatz achieves high pressure fuel injection. Each individual cylinder is fitted with a fuel pump/valve combination in a single housing, mechanically activated by the camshaft, which injects fuel at a very high pressure (1000 Bar) into the cylinder, thus dispensing with the need for a common rail.

New Engines

Engines in the 130 to 560 kW powerband have been available for some time – many were launched at Bauma 2004 – to give equipment manufacturers time to incorporate them into the machines that are now being launched in Europe.

Caterpillar's latest addition to its Stage IIIA compliant engine range is the C4.4, a four-cylinder engine that will be available in mechanical and electronic versions. The mechanical version of the C4.4 includes a two-valve head, rotary fuel injection pump, a single vee-belt design and optimised inlet manifold temperatures. Available in naturally aspirated, turbocharged, and air-to-air aftercooled configurations, the engine offers power outputs ranging from 56 to 90 kW. The electronic fuel management version is available with outputs from 75 to 112 kW.

New from Cat's subsidiary Perkins is the 3-cylinder 1103 D engine, which completes the 1100 Series. This now comprises engines from 37,5 to 205 kW. The 1103 D will be available in three variants – naturally aspirated, turbo charged and turbo air-to-air charge cooled – offering a choice of outputs from 37,5 kW for the naturally aspirated model to 65 kW for the 1103 D-33TA version.

A key part of the design concept has been to keep the engine envelope and major hook-up points as close as possible to the Stage II version, in order to make it for manufacturers to incorporate it into their designs. The engine's heat rejection characteristics are also little changed, which means minimal impact on current fan and cooling pack designs.