Citing growing evidence that dieselengine exhaust can cause serious health problems, the U.S. Environmental Protection Agency has issued regulations that will dramatically reduce emissions from off-highway diesel vehicles. The EPA considers these engines a major source of harmful particulate matter, as well as NOx, hydrocarbons, and other ozone-forming compounds.
The standards cover diesel engines used in a range of construction and agricultural equipment, such as excavators, bulldozers, logging equipment, and farm tractors. The regulations are structured in three decreasing levels, with each Tier involving a phase-in, by horsepower rating, over several years. The first Federal standards for off-road diesel engines were adopted in 1994 and were phased in from 1996 to 2000. Tier 2 standards take effect from 2001 to 2006, and more stringent Tier 3 standards phase in starting in 2005.
As just one point of comparison, Tier 1 standards mandate maximum NOx levels of 9.2 gm/kW-hr for engines over 300 hp, while Tier 2 and 3 levels for combined NOx and HC are 6.4 and 4.0 gm/kW-hr, respectively — nearly a 60% reduction.
The standards have forced engine manufacturers to take a close look at the nuances of diesel combustion. As a result, they are increasingly turning to sophisticated onboard controls to get the most power and efficiency out of each drop of fuel, with as few harmful by-products as possible.
" Cummins Inc., Columbus, Ind., will meet Tier 2 emissions standards with mechanical and electronic versions of its B and C Series engines for off-highway applications in the 60 to 340-hp range. But the company foresees a growing reliance on electronic controls to meet increasingly tougher regulations, says Bharat Vedak, vice president of Industrial Customer Engineering.
For instance, the company's Quantum System uses proprietary electronics to manage fuel delivery and combustion. An onboard computer takes in information on how the engine is operating, such as engine speed, boost pressure, and crank position. Algorithms compare engine status with desired operation (throttle position, speed, and torque limits) and translate that into output commands that physically control the fuel quantity, pressure, and timing (start of injection) for top performance.
The Quantum system works with all electronic fuel systems used on Cummins' engines. The CAPS fuel system, for example, is a high-pressure, common-rail type of fuel system that consists of:
- A high-pressure fuel pump.
- A high-pressure accumulator capable of decoupling pumping action from the injection process.
- An electronically actuated injection-control valve that accurately controls the start of injection and fuel quantity.
- A rotary distributor that hydraulically connects, in engine firing order, the injectioncontrol valve to injection nozzles in the engine cylinders.
The company's six-cylinder QSC line, rated from 240 to 340 hp, is one example of an engine using Quantum System electronic controls and the CAPS fuel system. The system provides high injection pressures independent of engine speed, along with precise timing and fueling control. This optimizes engine performance to meet emissions levels regardless of speed and load conditions. The system also produces a wide range of torque and power curves to meet various application needs — a capability not found on mechanical fuel systems.
The QSC features a 24-valve design. Four valves per cylinder provide efficient intake and exhaust. More air enters the cylinder, letting a larger amount of fuel to be injected and the engine to develop more power. Four valves also permit a vertical, centered injector. This develops a better fuel-spray plume and generates less spray over, lowering particulate emissions.
Cummins also announced that it can meet Tier 3 emissions standards with existing combustion technologies and hardware, and will launch engines prior to the 2005 standard.
According to Vedak, many manufacturers have been exploring two avenues to meet Tier 3 standards: cooled exhaust-gas recirculation and exhaust-aftertreatment devices such as catalysts. These involve costly redesign of existing vehicle platforms to accommodate additional hardware, he says.
Cummins reportedly can meet Tier 3 standards using existing engine platforms with electronic fuel systems, by refining control of the in-cylinder combustion process. This eliminates expensive and unproven aftertreatment devices, using fuel that can include up to 5,000 ppm of sulfur. Sulfur has been proven to significantly degrade certain aftertreatments. The result will be emissions-related changes at Tier 3 virtually transparent to OEMs and users.
Among the latest Tier 2 engines from Caterpillar, Peoria, Ill., is the 350-hp C-9, an 8.8liter, six-cylinder model. It features Caterpillar's ADEM (advanced diesel-engine management) III, an electronic-control module (ECM) that monitors engine conditions and precisely controls fuel delivery and combustion timing to minimize emissions. It adjusts combustion for different load and temperature conditions and can be programmed for warning, derate, or shutdown if needed.
The engine also uses Caterpillar's HEUI-B (hydraulically actuated, electronically controlled unit injector) fuel system to manage fuel-injection pressure, timing, and duration. Sophisticated electrohydraulic actuators control the injectors in this system. One advantage, according to Cat officials is that the HEUI-B system tailors injection rate to engine load and speed, optimizing performance across the entire operating range. The result is higher injection pressures, lower noise and emissions, and better fuel economy.
Electronic injection offers other advantages as well. It eliminates complex hydraulic governor linkages, which means fewer moving parts and a significant improvement in reliability and durability. Electronically adjusting fuel limits to maintain correct air/fuel ratios improves fuel burn and reduces particulate emissions and smoke. And the ECM's ability to match injection timing and duration with machine demand and a host of other sensed parameters cuts fuel consumption not only during steady-state operation but during transient acceleration as well.
It also includes features such as automatic altitude compensation that derates power for high altitudes (above 10,000 ft) to prevent excessive combustion temperatures and subsequent component damage. Low idle speed can be preset and timing retarded until the engine warms. If the operator increases throttle before the engine reaches operating temperature, electronic controls reduce the injection advance to provide continuous protection. The ECM also stores information on engine operation, giving an easy reference to diagnostic information if problems arise.
The C-9 features a four-valve, crossflow cylinder head for excellent breathing capability, which contributes to better fuel consumption and lower emissions. The head design allows for a centered, vertical injector to improve fuel-spray patterns, a significant factor in lowering exhaust emissions, according to the company.
Despite the demands on fuel economy stemming from the Tier 2 (and European Union Stage II) standards, the C-9 consumes about 10% less fuel at Tier 2 emissions levels than the company's 3306 engine at Tier 1 levels at the same power and speed.
HIGH EFFICIENCY Perkins Engines, Peterborough, England, recently introduced the 1100 Series, a new range of diesel engines conforming to Tier 2 and Stage II standards. The family includes a 3.3-liter three-cylinder engine available in naturally aspirated and turbocharged versions, six 4.4-liter four-cylinder engines ranging from 64 to 130 hp, and a six-liter six-cylinder turbocharged, air-to-air charged cooled unit that offers 174 hp at 2,400 rpm.
"Developing products on the basis of future market needs has resulted in engines exceeding the requirements of the new emissions regulations, while at the same time improving on every aspect of performance, reliability, and cost of ownership," says Michael Wright, marketing manager, new products.
The 1100 Series has been tailored specifically to meet this need with electronic engine controls optional on the four-cylinder engines and standard on six-cylinder models. In addition to reducing emissions and improving fuel consumption, electronic engine management also enhances performance, giving quicker response to operating conditions and customizing torque for better control. This new range is nearly 3 dB(A) quieter than the company's previous versions.
Other changes on the 1100 Series also contribute to cleaner combustion. The 1103/4 design integrates the inlet manifold into a crossflow cylinder head that precisely manages airflow. An improved cylinder-head design has also been introduced on the 1106 engine. Its optimized swirl combustion system uses helical inlet ports, which improve airflow and efficiency. The induction system leads to more complete combustion and better performance while reducing emissions. Under normal operating conditions the models generate no visible smoke.
New PowerTech engines from John Deere, Waterloo, Iowa, feature an electronically controlled, high-pressure common-rail fuel system. The system controls injection to match operating conditions by regulating pressure, timing, and fuel rate. The engines are also equipped with central vertical injectors for cleaner combustion.
The engines offer application flexibility through a variety of electronic packages including multiple throttles, torque curves, speed settings, cruise control, and standalone or vehicle-integrated control-panel options. The electronics also provide engine protection and failure diagnostics while eliminating mechanical parts such as throttle cables and shutdown devices.
Both four and six-cylinder versions are engineered with four valves-per-cylinder to enhance airflow, improve efficiency, and increase power and torque. They are air-to-air cooled and at 2,400 rpm, the 4.5-liter 4045H delivers 174 hp and the 6.8-liter 6068H offers 275 hp.
"Our customers will benefit from the nearly 25% increase in power capability from our new 4045H and 6068H engines," said Roger DeWitt, manager of PowerTech Engineering. As such, the engines deliver more power than previous versions in a smaller package size, and are said to lower installed costs for OEMs and end users. "The engines are also tuned for superior low-speed torque that is up to 30% greater and specific fuel consumption that is at least 5% better than our two-valve engines," he said. PowerTech engines meet Tier 2 emission regulations, and will provide the capability to meet future emission regulations, said DeWitt.
Yanmar Diesel America, Buffalo Grove, Ill., recently released its TNV Series engines designed for construction and agricultural machinery, generators, and pumps. The new Series consists of indirect-injection engines rated between 14.3 and 28 hp, and direct-injected models rated from 29.4 to 85.8 hp. Depending on the engine, the company uses a variety of emissions reduction technologies. This includes a four-valve-per-cylinder structure to improve combustion and air-inflow efficiency on some engines. Others have the injection nozzle set at a larger angle than usual for more consistent atomization and mixing. The combination improves combustion efficiency and startability while reducing noise and emissions.
All DI engines feature reentrant-type combustion chambers with high-efficiency swirl. New fuel-injection pumps feature higher injection pressures, a monoplunger that minimizes uneven injection at the cylinders, a timing device to control injection under various speeds and loads, and a constant-pressure valve to reduce speed variation at low throttle while optimizing fuel use.
The new 914 engine family from Deutz Corp., Norcross, Ga., meets EPA Tier 2 standards and, according to the company, demonstrates a bright future for air-cooled engines. Based on the company's 912 and 913 Series, of which more than 3 million have been manufactured, the 914 was conceived with future emission standards in mind. Dimensions and configuration of the 914 are almost identical to those of the 912/913 engine family, for near-seamless changeout.
The 914 is available with three to six cylinders, in power ranges from 32 to 190 hp. Stroke has been increased slightly and a new fuel system delivers injection pressures to 1,000 bar. Another important change is the position of the injection valves. They now project into the combustion chamber at a 10° angle relative to the cylinder axis, considerably steeper than before. These measures trim pollutant emissions relative to the 912/913 at the same average fuel consumption. In addition to diesel fuel, the 914 is suited to biodiesel and can be run with XF-63 jet fuel.
CLEAN AND QUIET
What comes out the tailpipe isn't the only emissions issue facing engine manufacturers. Customers are demanding quieter products as well. Vehicle noise is a complex issue that must consider the engine, transmission, hydraulics, fan, and other sources. In its 1100 Series, Perkins Engines has focused on reducing engine noise from three primary sources.
The first is force noise created by combustion and moving engine parts. The company modified the combustion process to reduce source noise and installed a quieter front helical gear train that has more teeth and tighter tolerances.
Another contributor is a new balancer design on four-cylinder engines and a new crankshaft on the three-cylinder that reduce vibration, important for low-noise operation.
The second source is transmission noise carried through the engine structure. To reduce transmission, Perkins stiffened the block structures while introducing an open top deck block on three and four-cylinder models. This places a layer of water between the cylinder and block exterior, effectively double-glazing combustion noise.
The final source is radiation noise which escapes the engine. To minimize escape, Perkins developed sound-insulating front covers and isolated top covers, while the three and four-cylinder units also benefit from an integral inlet manifold. Reduction on the four-cylinder model are 3 dB(A), effectively halving engine noise.