Geometric and Topological Considerations to Maximize Remotely Mounted Cylinder Pressure Transducer Data Quality 2009-01-0644

The piezoelectric cylinder pressure transducer is ubiquitous for developing and optimizing the combustion process in modern internal combustion engines. Over the past three decades, significant advances in cylinder pressure transducer technology and enormous advances in digital computing sophistication have made the acquisition and analysis of engine cylinder pressure the cornerstone diagnostic tool for today’s engine combustion community. Such improvements in the ease of acquiring cylinder pressure based metrics have, in many instances, fostered the assertion that the transducer is faithfully indicating the actual in-cylinder pressure. Careful analysis, however, can uncover anomalies in the cylinder pressure data quality resulting from thermal shock [1].

Randolph [2] laid the foundation for General Motor’s pursuit of remotely mounted piezoelectric cylinder pressure transducers, with fresh approaches to connecting passage design and the thermal protection of the transducer diaphragm. This paper builds on that foundation by introducing additional parameters affecting thermal shock. The effect of cylinder pressure increasing after flame arrival at the transducer passage is a primary factor assessed. These new techniques have been applied to combustion system development programs in the pursuit of research quality data for general spark-ignition engine development, and have improved our cylinder pressure data quality as an organization.

The concept of radius fraction burned as a technique for the topological accounting of the propagating flame front, and it’s interaction with the connecting passage and transducer cavity volume is introduced. Simplified analysis techniques to allow the combustion engineer to select appropriate mounting locations and thermal protection treatments are presented. Comparison of the simplified estimation to VisioTomo and Ion Probe Head Gasket data are also shown.

The critical volume ratio between the flame shield passages and transducer tip cavity as a function of in-cylinder pressure at flame arrival divided by peak cylinder pressure is also developed as a technique to prevent hot burned gas products from contacting the transducer face. Characteristic contour plots are presented to guide the combustion engineer to an optimized measurement installation based on combustion phasing and sensor location.

Transducer selection and evaluation is limited to mounting packages that can be readily applied to modern, automotive SI engines. But, in our corporate experience, it is still possible to produce reference quality data with proper transducer mounting. The concepts herein should be applicable to any in-cylinder pressure measurement situation with a propagating flame.