The off-highway equipment industry is on a clear path to introduce machines with near-zero emissions, made possible using advanced engine technologies and integrated exhaust aftertreatment. As Cummins looks ahead, perhaps an even greater challenge for the engine manufacturer is to also achieve higher fuel efficiency for the next generation of clean diesel engines.
Clearly, this brings the obvious advantage of lower overall operating costs, but there are other benefits also in play here. By achieving lower fuel consumption, the engine industry can make a positive contribution to two national initiatives—first, by reducing the carbon footprint of equipment and, second, by reducing dependence on foreign sources of oil.
Performance enhanced for Tier 4
The results from a recently conducted Cummins Tier 4 Fuel Duel test speak for themselves.
This test confirmed a 5% fuel efficiency improvement for a Cummins Tier 4 Interim QSB6.7 installation compared to an identical machine powered by a Tier 3 QSB6.7 engine. The fuel consumption evaluation was conducted under site conditions across a series of duty cycles representative of typical working operations.
Fuel Duel was undertaken to fully validate previous test results from other Cummins concept installations that have also demonstrated impressive reductions in fuel consumption while meeting U.S. EPA Tier 4 Interim and EU Stage IIIB low-emissions standards taking effect in 2011.
The 6.7-L QSB engines competing back-to-back in the Fuel Duel were specified with the same power output, peak torque, and rated speed. The higher fuel efficiency of the Tier 4 Interim engine was achieved without compromising machine performance. In fact, the Tier 4 Interim QSB6.7-powered machine completed the Fuel Duel tests within shorter cycle times due to a faster engine response to load demands. Thus, OEMs can expect lower cost of operation and enhanced productivity from their Cummins-powered equipment while achieving Tier 4 Interim low-emissions standards.
The 5% higher fuel efficiency achieved by the Tier 4 Interim QSB6.7 installation factored in active regeneration of the self-cleaning Cummins Particulate Filter exhaust aftertreatment. This was barely measurable in terms of fuel consumption, as the filter proved capable of self-cleaning in passive regeneration mode for long periods of the equipment operating time.
So how was this improvement in fuel efficiency and engine response achieved while at the same time reducing PM by 90% and NOx emissions by 45% to meet Tier 4 Interim standards? An important element here is the capability to design and manufacture the complete engine system from air-in to exhaust-out aftertreatment, meaning we can leverage our integration advantage to formulate a cleaner and more fuel-efficient combustion process.
When we look at some simple math, we can see how this translates into reduced operating costs. Using an example of 10,000 gal (37,900 L) of fuel consumed by a Tier 3-powered machine each year, this could save up to $1000 for the operator using an equivalent machine powered by Cummins Tier 4 engine (based on an estimated cost of $2 per U.S. gallon). By 2011, the cost savings could be even more significant with higher costs per U.S. gallon expected and potentially even higher in the EU. Less gallons consumed also means less oil to import, benefiting the national economy.
Using the same example, the 5% fuel savings could typically eliminate up to 6 ton (5.5 t) of CO2 greenhouse gas emissions from a Cummins Tier 4-powered machine each year. To further contribute to CO2 emissions reductions, all Cummins Tier 4 engines will be capable of operating on B20 biodiesel fuel blend.
To help OEM customers achieve the best possible fuel efficiency for their equipment, Cummins has introduced a virtual fuel consumption service available on a consultancy basis to predict Tier 4 Interim fuel savings for specific duty cycles and machine types. The analysis work is undertaken by Cummins Virtual Installation Center, recently established to support OEMs with Tier 4 integration work.
Opportunities for fuel savings can be identified for the machine before work commences on the prototype installation. In this way, we can fine-tune various machine and engine features at the virtual design stage to realize the best possible fuel efficiency.
Generating hybrid efficiency
Requirements for higher fuel efficiency and lower carbon footprint are generating an interest in diesel-hybrid powered equipment. Cummins is a leading supplier of engines for on-highway diesel hybrid installations and our expertise is ready to transfer to the off-highway equipment industry.
We can see this with the Cummins B3.3 engine that powered the Mecalac 12MTX hybrid wheeled excavator to environmental award-winning success at Intermat in Paris. The 68-hp (51-kW) rated four-cylinder B3.3 engine drives an electrical generator and lithium-ion battery system to achieve 25% lower fuel consumption with much reduced CO2 emissions and quieter operation. The 12MTX demonstrates how higher fuel efficiency and lower emissions can be achieved with innovative engineering. Compact and agile, the 9-ton (8-t) diesel hybrid is suited for city center construction sites with limited operating space.
The B3.3 engine is directly coupled to a 20/40-hp (15/30-kW) Heinzmann electric motor generator that is attached to the hydraulic pump as a common drive, with the engine requiring no starter or alternator. The diesel-electric powertrain operates at an engine rpm speed optimized for fuel efficiency and charges the 400-V lithium-ion batteries that store the electric power. During machine braking, energy is recovered and transferred to the batteries.
The 68-hp mechanical power of the engine output is rated to match the average power requirement of the machine. When less than 68 hp is needed, the batteries are charged; when more is needed, the electric motor provides additional power up to 99 hp (74 kW). A power loop electronic control system ensures a seamless power adjustment between diesel engine and electric motor. Importantly, the diesel-electric hybrid architecture is designed to be simple and easy to maintain.
While these are still early days for diesel hybrid machines, the technology does offer real possibilities for the industry that will complement the introduction of Tier 4 ultraclean equipment. By achieving significantly reduced fuel consumption, this provides a key driver to develop the technology.
Leveraging the on-highway experience
As emissions regulations have become more and more stringent, the engine technologies required to meet them have become increasingly complex. Similarly, the introduction of diesel hybrids brings a new complexity into the equipment market. While these technologies are new to the off-highway industry, they are not new to Cummins.
Over a number of years Cummins has developed a broad technology product portfolio including Cummins Fuel Systems, Cummins Turbo Technologies, Cummins Filtration, and Cummins Emission Solutions. Experience drawn from integrating all of these components for the on-highway business will now be used in the off-highway sector as emissions level and demands for fuel efficiency and a lower carbon footprint become more aligned. In fact, the component technologies are so successful they are used not only with Cummins engines but also are supplied to other engine manufacturers.
As we look ahead to Tier 4 and beyond, the technology challenge for the industry remains significant, but the road map to achieve it is becoming clear. The rewards in terms of higher fuel efficiency, improved machine productivity, and environmental improvements will make this an exciting journey.
Hugh Foden, Executive Director, Off-Highway Business, Cummins, wrote this article for SAE Off-Highway Engineering.