A new engine for the Asian market meets emissions control regulations
By Mark Tussing, Marc Megel and David Branyon
In the global effort to reduce automotive emissions, Asia is emerging as the region with the greatest potential for improvement using available technologies. Air pollution levels in Asian countries can be orders of magnitude higher than in the West. As the United States and other western nations push the envelope on engine emissions technology, China and other Asian nations are clamoring to catch up. One result is that engineers and scientists at Southwest Research Institute (SwRI) find themselves designing newer and vastly improved engines for the Chinese market.
Looking to the future
In January 2005 SwRI initiated a project with Shanghai Diesel Engine Company (SDEC) to redesign and develop its D9 diesel engine to achieve future mandated Asian emissions levels. At the same time, SDEC also sought significant improvements in the engine’s power, durability and fuel economy. At the time, this project was the largest in scope among a growing number of projects that SwRI has conducted for the Chinese engine industry.
The starting point was an 8.3-liter diesel truck engine that SDEC designed in the early 1990s with input from a European consulting company. While that engine, which was similar to an early 1980s U.S. diesel design, met the current Chinese emissions levels of Euro II, it would not have achieved the next level of emissions legislation (Euro III) without significant changes. SDEC did not want to invest in the changes required for Euro III without considering emissions requirements that would be in place during the next 10 years. That meant SwRI engineers would have to redesign the engine so that the base design was capable of achieving Euro IV and Euro V emissions requirements as well.
While some engine design changes obviously are necessary to reduce emissions, the fundamental level of redesign required is not as obvious. To provide SDEC with an engine that would perform adequately 10 to 15 years into the future, the SwRI team had to redesign every major component with the exception of the crankshaft. Complicating the design effort was an SDEC-imposed constraint requiring that the new engine be manufactured using many of their existing manufacturing facilities and tooling. The SwRI team essentially undertook the design of a new engine to be built in an existing manufacturing facility.
Performance design changes
Any engine design and development project has two major considerations: performance, which includes power, emissions and fuel consumption; and durability, which includes the reliability and structural capability of the engine components. In this case, the most significant design requirement was the redesign of the cylinder head. Achieving better emissions at higher power levels, while maintaining reasonable fuel efficiency, required changing the head design from two valves per cylinder to four. This change not only increased air-flow but also allowed the fuel injector to be placed in the center of the combustion chamber. The centralized injection point is critical to lower emissions because the fuel can be distributed evenly throughout the combustion chamber. Improving combustion for reduced emissions also means higher injection pressure for the diesel fuel, along with improved control of the injection event — or even the number of injection events, in cases where multiple injections of fuel during the same engine cycle are required. For the SDEC project this meant exchanging an antiquated, mechanically driven fuel system for a more modern, electronically controlled, high-pressure common-rail fuel system.
The fuel system change, in turn, necessitated a complete redesign of the front-end gear train because the drive ratio for the electronic fuel system pump is double that of the old mechanical system pump. The gear train is a major source of noise on a diesel engine, so special consideration was made for the design of the gears and the gear housing. Overall, engine noise was reduced by 6 decibels (dB) compared to the Euro II version of the engine, mostly attributable to changing the fuel system and redesigning the gears and gear housing.
Durability design changes
One of the hidden implications of improved engine emissions and performance is that the peak firing pressure of combustion increases. This increase has a direct effect on the loads applied to a majority of engine components. In the case of the SDEC D9 design, the cylinder block, cylinder head, pistons, connecting rods and bearings all had to be redesigned to handle the higher pressures required to achieve not only Euro III standards, but also those expected under Euro IV and Euro V. The increase in firing pressure to achieve Euro III was roughly 18 percent; Euro IV and V are estimated to require an additional 30 percent increase. Therefore, the design targets for the D9 had to take into consideration a 50-percent total load increase due to firing pressure.
The SwRI team conducted extensive design analysis on all of the major components to ensure the new design would be reliable at future emissions levels. The cylinder block was modified for improved structural durability. Improvements also were made to reduce noise transmitted and radiated by the cylinder block. The most complicated component, the cylinder head, was designed using technology and know-how from SwRI’s experienced design team. The valvetrain and gear drive system were completely redesigned using modern dynamic system simulation techniques, combined with iterations of the thermodynamic modeling required to maintain engine performance targets.
Developing the final product
SwRI fired the first prototype engine for SDEC in February 2006, roughly a year after the project began. Within the first week of running, the engine achieved the power, fuel efficiency and emissions targets set out by the customer. The targets were globally competitive for a Euro III truck engine.
In addition to establishing performance characteristics, SwRI engineers conducted numerous mechanical development tests on the engine and on a number of major engine components, such as the cylinder block and cylinder head. These tests verified analytical work done during the design of the engine and demonstrated the durability limits for major engine components and systems.
SwRI performance development specialists went on to increase the engine’s power by an additional 5 percent for the final calibration, exceeding the customer’s target that called for a substantial power increase over the Euro II version. SDEC contracted with SwRI for an additional project in 2006 to demonstrate Euro IV capability with the engine. The development team successfully demonstrated Euro IV emissions levels and went on to achieve Euro V as well, again exceeding the customer’s expectations.
Global engineering team
SwRI has been building an experienced engine design and development team for a number of years. The SwRI team includes numerous engineers with previous long careers at major engine companies. In addition, SwRI established an exclusive partnership in 2002 with Powertrain Technology Ltd. (PTL), a small engine design company in the United Kingdom. PTL is a team of approximately 10 engine design and analysis engineers who work as an integrated part of SwRI’s Design and Development Department.
SwRI also integrated SDEC’s design staff into the D9 project team. For two months during the design phase, a team of 12 engineers from SDEC worked on-site at SwRI. They received training and guidance from SwRI engineers and experienced the engine design process firsthand. A smaller team of SDEC engineers also was present at SwRI for the performance and mechanical development phases of the project. SwRI continued supporting the client through production launch.
When SwRI and SDEC officials signed off on the project in March 2008, the venture substantially exceeded initial requirements. SwRI was able to successfully deliver a diesel engine that meets SDEC’s current and future needs by providing a design that can help cut automotive emissions in Asia, thereby helping tackle air pollution in that part of the world.
Questions about this story? Contact Megel at (210) 522-3079 or email@example.com.
Published in the Summer 2008 issue of Technology Today®, published by Southwest Research Institute. For more information, contact Joe Fohn.