Peterborough, UK--Once considered the rough-and-ready workhorse of industry, the diesel engine is shedding the reputation of smelly, clattering machine. While legislators turn their attention to emission control for off-highway vehicles, engineers are creating elegant powerplants that don't sacrifice the hallmark diesel endurance and reliability.

At diesel-engine-maker Varity Perkins, engineers look beyond pollution control to engine designs that purr instead of roar. The firm is a quiet presence in North America in more ways than one; Perkins' engines go to work in the U.S. and Canada wearing several different badges. For example, the company has a 20-year-old partnership with Caterpillar, and counts Chrysler and materials-handling equipment manufacturers Hyster and Clark among its customers. Alliances with Detroit Diesel and Navistar add to U.S. operations.

In all, the company estimates a million Perkins engines are operating in North America, powering on- and off-highway vehicles, agricultural, industrial, marine, and military equipment.

Now, there's a small but spunky new engine in the lineup: the Perkins 700 Series. Created to power forklift trucks, compressors, compact agricultural tractors, and construction equipment, the engine is the result of a joint effort with Iseki of Japan.

Engineers at Perkins and Iseki knew that several features were "musts" for customers in these applications: compact size, flexibility for use in a range of equipment, and ease of maintenance. With emissions regulation looming, many customers wanted the new engine immediately.

"Machine designers around the world have told us that they need different answers to meet emission controls and to satisfy the increasing demands of their customers," says Perkins Group Chief Executive Mike Baunton. Adds Perkins Design Manager Adrian Heath, "designing, developing, and producing engines of this sophistication would normally take between three and four years--a highly expensive process. Perkins 700 Series engines took less than two years."

Heath credits the speedy development to 3-D FEA and CAD software such as I-DEAS from SDRC and proprietary predictive tools. Flexible manufacturing allowed the designers to overlap engine development and manufacturing to a greater extent than normal, he adds.

The 700 Series are naturally aspirated four-cylinder, four-stroke, liquid-cooled engines. Engineers created a choice of swept volumes to deliver several engine options in the same compact profile. The engines come in both a 2.6-l indirect-injection model (704-26), and a 3.0-l direct-injection version (model 704-30).

The 2.6-l engine, rated at 58 hp (43 kW) at 2,600 rpm, has a maximum torque of 160 Nm at 1,600 rpm. Engineers configured this engine specifically for material-handling applications.

Although it looks identical on the outside, the 3.0-l version, rated at 63 hp (47 kW) at 2,600 rpm, has maximum torque of 210 Nm at 1,600 rpm. This engine is tailored for off-highway applications such as small agricultural equipment and construction machinery.

Direct-injection finesse. Fuel-air management is essential to low emissions and combustion efficiency, so improvements to engine breathing were first priority to Perkins engineers. "No aspect of combustion was ignored," recalls Perkins Environmental Engineering Director Tony Downes. For instance, a closed-circuit breather separates any oil vapor resulting from crankcase pres-surization. Recovered gases are fed to the induction manifold, and oil droplets return to the lubrication system.

To optimize swirl and flow characteristics, en-gineers designed new inlet and exhaust ports. They paid particular attention to the 3-l en-gine's direct-injection inlet port, which is a highly efficient helical system. "The design calls for relatively large valves, operated by a new valve train to achieve good valve lift characteristics and long life over all duty-cycles," says 700 Series Project Manager Brian Hood. New manifolds improve air flow and contribute to a compact package. For the 2.6-l engine, a pre-combustion chamber allows the engine to operate without visible smoke--an important characteristic for indoor operation.

Both engines use a cassette-type fuel-injection pump, housed in the cylinder block and supplied by UK-based Zexel. Like many suppliers in the program, Zexel and Perkins engineers teamed to develop the pump's hydraulic specifications, which also helped to trim the development cycle.

The entire fuel system--including the injection-pump cassette with its electric shut-off solenoid, injectors, and high-pressure pipes--are on the right-hand side of the engine for easy maintenance. The lift pump, fuel filter, and low-pressure pipes are also conveniently located together. "Users will like the one-side servicing layout," predicts Hood. "This feature is especially important in the construction sector, where transverse installations make it a requirement."

The 704-30 uses two-stage injectors that give it some car-like qualities, including lower emissions and a noise rating of 94 dBA, claims Heath. The injectors soften combustion noise by injecting fuel slowly at first, then, when burning has started, injecting more rapidly into a re-entrant combustion chamber. "This lowers the rate of pressure rise within the cylinder and noise," adds Heath. Because the re-entrant style combustion bowl encourages air-fuel mixing, it also improves emissions.

Engineers chose aluminum alloy pistons to minimize reciprocating mass, vibration, and noise. Silicon-carbide honed bores, paired with a set of three low-friction rings, provide efficient gas sealing and boost oil control, which also contribute to emission performance.

Today, production of the new engine is approaching 50,000 units per year. Both models surpass worldwide Stage I off-highway emissions standards due to be implemented in Japan, the U.S., and Europe between 1997-1999. Perkins has vowed that turbocharged and spark-ignition versions will be added in the future.

Currently, the market for this size engine totals between 130,000 and 140,000 units; Perkins aims to stake out a quarter of it by the year 2000.

"The 700 Series is a true, purpose-designed industrial and agricultural diesel engine, not a vehicle engine diverted to this market from spare capacity," says Baunton. "With a compact profile suiting today's trend towards smaller machines, customers will find the 'engineering in' of Perkins 700 Series will be simple."