Diesel engines boast such excellent features as reduced CO2 emissions to which global warming is widely attributed. However, diesel engines emit nitrogen oxides (NOx) and particulate matter (PM), and concerns regarding their impact on the atmosphere and human body have fueled demand for the development of “clean” diesel engines that dramatically reduce these substances.
NOx is emitted during high-temperature combustion, while PM tends to be emitted when attempting to reduce NOx. This makes the reduction of both substances, while improving fuel efficiency, an immense technological challenge.
As shown on page 16, Tier III regulations for off road engines will be phased in from 2006 in such areas as the United States (Tier III) and Europe (Stage IIIA). The U.S. Environmental Protection Agency (EPA) plans to implement Tier III regulations from 2006 that call for a 40% reduction in NOx compared with Tier II regulations. There is a strong emphasis on reduction of off-road diesel engine emissions from construction equipment, particularly for engines used in heavy-duty (high-revolution, high-load) operations,which is a main factor underpinning increased technological development targeting construction equipment.
Building on more than 70 years of experience in off-road engine development for construction and mining equipment, Komatsu is able to design high quality engines that optimize machine functionality by leveraging a wealth of accumulated technologies and expertise as an equipment manufacturer.
In meeting the deadline for implementation of these regulations starting from 2006, Komatsu will be gradually releasing a new Tier III (Stage IIIA)-compliant engine from 2005 that combines reduced NOx and PM emissions with improved fuel efficiency.There are several notable features to these engines as follows.
1. Heavy-Duty High-Pressure Common Rail (HPCR) Fuel Injection System
Komatsu incorporated a heavy-duty High-Pressure Common Rail (HPCR) fuel injection system in designated Tier (Stage) II diesel engines to achieve both NOx and PM reductions and better fuel efficiency.The newly developed engine will see further improvement in heavy-duty HPCR functionality and more widespread application.
Specific features of the heavy-duty HPCR fuel system are its ability to inject high-pressure fuel accumulated in the common rail into the combustion chamber, thus atomizing fuel spray and optimizing combustion for better fuel efficiency, lower emissions and higher performance. Another feature is its flexibility to maintain the optimal fuel injection volume, pressure and timing through precision electronic control. This results in near complete combustion, contributing to PM emissions reduction and dramatically improved fuel efficiency.
The heavy-duty HPCR fuel system also reduces engine noise by compartmentalizing injection in a multi-staged injection process and enables high low end torque on account of its high-precision fuel control and flexible, high-pressure capability regardless of engine speed.
Komatsu was among the first construction equipment manufacturers to apply HPCR technology to Tier (Stage) II engines. Given its ever-wider application in trucks and automobiles since 1995, especially in Europe, HPCR is virtually the global standard for trucks and automobiles. For Tier III (Stage IIIA) engines, the fuel system has been upgraded and fuel Heavy-Duty HPCR
injection pressure of up to 1,800 bars can be achieved compared with 1,400 bars for Tier (Stage) II engines. In addition, more durable supply pumps, injectors and systems are employed to withstand any harsh conditions around the world. The Komatsu heavy-duty HPCR fuel system is likely to become the global standard for off-road heavy-duty machinery in the near future.
2. Heavy-Duty Cooled EGR (Exhaust Gas Recirculation)
Komatsu is one of the front runners in the construction and mining equipment industry to use the heavy duty cooled Exhaust Gas Recirculation (EGR) system in medium and large engines, which is effective in lowering NOx without sacrificing fuel economy.In the heavy-duty cooled EGR system, a portion of gases emitted from the engine is cooled through the
EGR cooler, and it is diverted into the cylinder as inert gas. This feature reduces the concentration of oxygen in the combustion chamber, and thus, the combustion temperature and NOx. Further, this system can reduce NOx without retarding fuel injection
timing. Cooled EGR is considered the best technology for reducing NOx in diesel engines, and most of the leading engine manufacturers have employed cooled EGR with resounding success in engines that meet stringent on-road engine regulations since 2002.
Komatsu has developed the innovative high capacity heavy-duty Twin-Valve Cooled EGR system in light of the rugged and high-load usage of construction equipment and industry regulations. Key features include a Twin-Valve EGR system with intake air bypass for high-load and wider speed- range usage (patent pending); highly reliable and durable,high-precision electronic-controlled hydraulic twin valves; and a highly durable EGR cooler for operation in rough environments.
Komatsu took advantage of its long-established Heavy-Duty Cooled EGR engine technologies for construction equipment. Tens of thousands of hours of bench tests and field tests have been conducted to assure quality for maximum reliability and durability. In consideration of heavy duty usage and various conditions all over the world,Komatsu employed extra-thick, corrosion-resistant materials in the EGR cooler.
The cooled EGR technology is bound to become the global standard in construction equipment engines, and will undoubtedly be featured on the next Tier IV (Stage IIIB) line of engines.
3. Total Electronic Control
Komatsu has employed electronic controls in the new engine to enable total control over the equipment,such as variable horsepower control, hydro-static engine control and torque-converter engine control.Variable horsepower control, for example, selects the optimal fuel-consumption map and output of construction equipment in accordance with actual condi-
tions. This is the kind of technology that Komatsu, as a manufacturer of both engines and equipment, has the proven capability to develop.
4. Combustion Technology
Several improvements have been made in the combustion chambers for better air/fuel mixing and optimal combustion. For small engines, in addition to employment of HPCR technology, a four-valves-per-cylinder design is applied so that the fuel injection nozzle is placed in the center of the combustion chamber, enabling much greater optimal combustion.
5. Air-to-Air Charge Air Cooling
The air-to-air charge air cooling system is effective for lowering the charge air temperature to inhibit NOx emissions without sacrificing fuel economy.For this reason, more Tier III (Stage IIIA)-compliant engines will be fitted with this system.
In the years ahead, Komatsu will strive for technological innovation in further developing low-emissions engines in preparation for future environmental regulations, while providing global customers with products that are both ecological and economical.
Sumber : Komatsu VIEWS Magazine