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Mechanical Engineering, Feb 2001 by Hutchinson, Harry

Researchers at Purdue University in cooperation with Ford Motor Co. have developed a system that can maintain an engine's fuel ratio to control tailpipe emissions.

The system is designed to predict and provide the amount of fuel needed to keep the optimum air-to-fuel ratio of 14.1:1.

According to Matthew Franchek, an associate professor of mechanical engineering who led the Purdue research team, that ratio is the "sweet spot" at which the internal combustion engine's catalytic converter does its best work in breaking down emissions and reconstituting them as water, carbon dioxide, and nitrogen.

The fuel control system uses the sensors and the computer already on board the vehicle. "We're only changing software," Franchek said.

The team worked with a Ford engine, a 4.6-liter V-8 with fuel injection, at Purdue's graduate student research labs, the Ray W. Herrick Laboratories in West Lafayette, Ind. What distinguishes the Purdue approach from other control systems is that the engine computer contains mathematical models that predict the amount of fuel needed based on airflow into the engine.

At the front end, the engine's computer receives information from sensors that monitor mass airflow and engine speed. The computer uses that information to reach a calculation of how much fuel is needed to maintain the best ratio. The system can also work with a manifold air pressure sensor in place of the mass airflow sensor, Franchek said.

The computer controls the fuel flow to keep the right volume coming, and then checks up on itself through an exhaust gas sensor. This can be either a heated exhaust gas oxygen sensor or a universal exhaust gas oxygen sensor. If the exhaust reading indicates that the air/fuel mix is too rich or too lean, the computer will adjust.

According to Franchek, the system has been demonstrated at Purdue and has been taken in-house at Ford.