Homogeneous Charge Compression Ignition Engine Controls
with In-Cylinder Ion Sensing, 03-9385

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Principal Investigators
Yiqun Huang
Darius Mehta
Ryan Roecker

Inclusive Dates: 04/01/03 - 04/01/04

Background - Recent research activities have greatly expanded the understanding of Homogeneous Charge Compression Ignition (HCCI), its controlling mechanisms, and HCCI engine operation strategies. However, substantially more work is required before HCCI engines will be ready for production. This includes development of a methodology for feedback and closed-loop control of the fuel and air systems to keep the combustion optimized over the load speed range in a production vehicle. HCCI engines used in the laboratory can use custom prototype hardware, which includes expensive cylinder pressure transducers that are not practical for usage on mass production engines.

In this project, we use in-cylinder ion sensing to extract the timing of 50% burning rate and peak pressure and monitor other combustion information such as knocking and misfire as feedback signal to perform closed loop control of HCCI engines. The ion sensor we use is modified from the existing glowplug of each cylinder.

This method will minimize the cost of expensive in-cylinder pressure sensor and signal conditioning circuitry while providing equivalent combustion information for ECU to control the engine. It is simple, practical, and inexpensive. It makes the HCCI engine closer to mass production application.

Approach - Three objectives have been identified to accomplish the project. First, the affecting parameters on ion signal will be identified and ion signal-timing of 50% burning rate and timing of peak pressure correlation will be established, which is valid for HCCI engine control. Second, the correlation will be used to control one parameter-- injection timing of the HCCI engine. Third, the results from in-cylinder ion sensing based control strategy will be compared with that of in-cylinder pressure sensor based control strategy.

Accomplishments - To evaluate the feasibility of sensing the combustion using ion-sensing probe protruded into the combustion chamber, an ion-sensing probe was tested in a constant volume combustion bomb. The fast rising of the ion signal from the probe is with the same period of the fast increase of the bomb pressure. The location of the peak of the ionization signal is very close to the peak of the cylinder pressure. Both the uprising of the ionization signal and the location of its peak are the main parameters will be used in the engine control strategy.

The project team plans to conduct engine tests on a Duramax diesel engine operated at HCCI mode. The setup of the test engine is shown in Figure 1.

Figure 1. Test Engine Setup (left); the Ion Sensing Probe Installed in the
Glowplug Aperture (right).

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