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Liebherr particle filters protect people and the environment

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Liebherr’s robust, high-power diesel engines are used primarily in the company’s earthmoving equipment, mobile cranes and special machines. They are characterised by advanced technology and precise machining.

The four- and six-cylinder inline engines produced in Bulle (Switzerland) and the six- and eight-cylinder V-engines cover the power range of 200 to 500 kW. A combination of intelligent electronic design and advanced injection and exhaust recirculation technologies not only ensures compliance with European emission regulations, but also forms the basis for fulfilling even more stringent requirements in the future. Very high fuel efficiency is achieved with modern common-rail diesel injection systems. However, these systems also lead to the production of extremely fine combustion and soot particles, which are only marginally captured by the motor oil. Soot and fine particles carried in the exhaust stream that end up in the environment can be harmful to health. For this reason, machines powered by diesel engines cannot be used in environmentally sensitive application areas such as tunnel construction or in closed buildings such as recycling plants unless they are equipped with a soot filter in the exhaust path. For approximately three years, Liebherr has offered suitable filters for OEM installation or retrofitting. 

One of the challenges in developing these particle filter systems for construction machinery is that they are essentially different from exhaust handling systems for diesel lorries due to different standards and requirements. In the latter systems, selective catalytic reduction (SCR) is used to reduce nitrogen oxide (NOx) emissions by approximately 90% (in stationary operation). Among other things, this is achieved by injecting AdBlue, a clear 32.5% solution of high-purity synthetic urea in demineralised water, into the exhaust stream. This urea solution, which is used at a rate up to 1.5 litres per 100 km, is held in a separate tank. It is sprayed into the exhaust stream ahead of the catalytic converter by a dosing pump or an injector. With the aid of the urea, the nitrogen oxides (NOx) are converted into nitrogen and water vapour in a chemical reaction. This “active” aftertreatment of exhaust gases to reduce nitrogen oxides for diesel engines in construction machinery is still a long way off.

However, AdBlue will become a current topic for mobile machinery as well by the time Level 4 of the Exhaust Gas Standard takes force in 2014. The primary task of particle filters for construction machinery is to reduce soot emissions. Liebherr’s designers have developed particle filter systems tailored precisely to the company’s construction machines. They are designed to withstand the severe conditions of construction site use, and they remove at least 97% of the soot and fine particles while reducing carbon monoxide (CO) and hydrocarbon (HC) emissions by 75 to 90%. Five filter sizes are available, corresponding to different engine power ratings. They can easily be adapted to the equipment, even in case of retrofitting. The systems are installed in place of the existing silencer, whose role they also assume. The system is integrated in the engine compartment. The Liebherr solution reliably avoids field of view restrictions, as is sometimes the case with equipment retrofitted outside the engine compartment.

Of course, even the best particle filters require maintenance. Although the retained soot particles are automatically oxidised by continuous passive regeneration when the exhaust temperature is greater than 250°C for at least 50% of the operating time, combusted or evaporated motor oil constituents containing metallic elements, such as calcium, phosphorous, zinc, sulphur or boron, remain in the filter module as deposits. These oil residues must be removed with all types of diesel particle filters (DPFs). If the low-ash Liebherr 10W-40 motor oil developed especially for use with DPF systems is used, the cleaning interval can be increased from an average of 1,000 operating hours to 2,000 operating hours. At the end of this interval, the filter module is dismounted and sent to a service centre, where it undergoes heat treatment in a special oven and is then cleaned.

In addition to the right motor oil with fewer ash-forming additives than conventional motor oils, fuel quality is a critical factor for proper operation and effectiveness. Only diesel fuel that has a sulphur content less than 50 ppm (0.005%) or complies with the EN 590 standard may be used. Heating oil, which usually contains considerably more than 1,000 ppm sulphur, would negate the effectiveness of the DPF and therefore cannot be used a fuel. It is essential to use a low-ash, low-SAPS motor oil, which means an oil with low sulphate ash, phosphorus and sulphur (see the “Question time” section of this issue for more information on low-SAPS motor oils). Liebherr low-ash 10W-40 motor oil is specifically formulated for heavy-duty diesel engines with particle filters and/or exhaust gas aftertreatment systems. It complies with the ACEA E4, E6 and E7 specifications and the US API CF-4, CG-4, CH-4 and CI-4 specifications. It is also specifically approved by leading engine manufacturers. However, it must be borne in mind that low-ash motor oils have a reduced alkali reserve (measured as the Base Number or BN) and therefore have less capacity for neutralising acids, which arise in greater quantity when sulphur-containing fuels are used.

Depending on the model, the engine of a construction machine holds 20 to 50 litres of motor oil. Based on field tests using engines with DPFs, Liebherr recommends changing the oil at fixed intervals of 500 operating hours. If the oil lifetime is exceeded without supplementary oil checks, there is a risk of engine damage due to increased viscosity and the formation of spongy deposits as a result of an increased concentration of soot particles in the motor oil, which contains fewer dispersants than conventional motor oils on account of the low-ash characteristic.

The experts in the Liebherr customer service department strongly advise against the use of a supplementary bypass filter for uncontrolled extension of the oil service interval. Experiments accompanied by oil analyses have repeatedly shown that the primary reason for the extended oil change interval is solely the increased oil volume resulting from the bypass filter.

The decisive factors for reliable engine operation and full effectiveness of the particle filter are regular checks and maintenance, the low-sulphur quality of the diesel fuel, and a low-ash, high-performance motor oil. Periodic oil analyses indicate whether the soot content of the motor oil has passed the critical 4% level and whether adequate amounts of dispersants are still present in the oil. For example, if an engine is filled with a motor oil that is not low-ash or a fuel with too much sulphur content is used with a low-ash motor oil, this can have negative effects on the engine and the particle filter. If anything goes wrong, OELCHECK can test the fresh and used oils, as well as the fuel, in its laboratory. This determines precisely whether an unsuitable lubricant or an unsuitable fuel was used. 

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