Using Ion Sensing with O2
Sensor-Based Adaptive Calibration to Perform
Cold Start Closed Loop Air/Fuel
Ratio Control to Reduce Engine
Cold Start Hydrocarbon Emissions, 03-9305
Principal Investigators
Yiqun Huang (Ryan
Roecker)
Joseph Grogan
Inclusive Dates: 04/01/02 - 04/01/03
Background - Currently, most gasoline engines are equipped with oxygen sensors to provide closed loop control of the air/fuel ratio. However, oxygen sensors have limitations. These sensors require approximately 30 seconds to warm up before accurate readings can be provided. The oxygen sensor is useless until it warms up, and 60 to 80 percent of total tailpipe hydrocarbon emissions are produced in the first 60 to 120 seconds after an engine cold start. During this interval, the air/fuel ratio is under open loop control and is not optimized. However, an ion-sensing spark plug, which detects ion signals, does not need this warm-up interval and can provide in-cylinder air/fuel ratio control as soon as the engine starts. Unlike other kinds of sensors, engine spark plugs are routinely replaced during periodic maintenance. In addition, production engines have many sources of variation and aging effects, so the technique of ion sensing for air/fuel ratio feedback requires online adaptive calibration to be successful.
Approach - This project aims to use a signal from a warmed oxygen sensor to calibrate ion-sensing spark plugs (ion sensor) adaptively. The goal of this project is to minimize over-fueling the engine during the warm-up transient of the federal test protocol driving cycle. The research team plans to use ion sensing to provide air/fuel ratio information that is fast enough to allow the electronic control unit to perform closed loop control during cold starts.
Three tasks will need to be completed for this project. First, affecting parameters, such as pressure and temperature, will be isolated, and an ion signal-air/fuel ratio correlation valid for cold start condition will be established. Second, the correlation will be applied to online calibration of the ion sensor air/fuel ratio signal using the original equipment manufacturer's O2 sensor signal during normal engine operation. Third, the calibrated ion sensing will be used as a feedback signal for the cold-start, closed-loop, air/fuel ratio control.
Accomplishment - To isolate each affecting variable, a constant volume combustion apparatus has been chosen to perform tests of the ion signal versus air/fuel ratio at different temperatures and pressures. The constant volume combustion apparatus test has confirmed that ion detection has a strong potential for in-cylinder equivalence ratio detection.
Constant volume combustion apparatus setup with ion-sensing ignition and detection modules
