Frederic Anton Matekunas

Cylinder-pressure-based engine control using pressure-ratio-management and low-cost non-intrusive cylinder pressure sensors

Over the last two decades, advanced engine control systems have been developed that use cylinder pressure as the primary feedback variable. Production application has been limited by cost, reliability, and packaging difficulties associated with intrusive cylinder pressure sensors. Now, a low-cost cylinder-pressure-based engine control system has been developed that utilizes Pressure-Ratio Management (PRM) and non-intrusive cylinder pressure sensors mounted in the spark plug boss of four-valve-per-cylinder engines. The system adaptively optimizes individual-cylinder spark timing and air-fuel ratio, and overall exhaust gas recirculation (EGR) for best fuel economy and lowest emissions over the life of each vehicle. This paper presents the engine control and cylinder pressure sensor systems. Results are presented showing spark timing and EGR control, knock and misfire detection, cylinder-to-cylinder air/fuel balancing, and cold start control.

Modes and Measures of Cyclic Combustion Variability

A single-cylinder engine with a transparent piston crown was tested with three intake geometries which produced different levels of swirl, and with two spark locations. A heat-release analysis was performed on the accumulated pressure-time data. Using this data base, relationships of maximum cycle pressure and its location in the cycle to the placement of the burn in the cycle are developed for different burning rates as a means of diagnosing sources of combustion variability. Among the significant observations were that combustion variability for operation away from the lean limit or incipient misfire is not strongly dependent on flow conditions at the spark plug and early flame behavior, but more dependent on the cyclic repeatability of the overall cylinder flow pattern. In the region of incipient misfire the early flame process becomes a significant source for variability. The onset of significant variability in IMEP corresponds to a condition where a collection of cycles shows the production of an increasing number of abnormally late burns as the spark is advanced. Additional spark advance results in the occurrence of misfire at approximately the frequency of the late-burn occurrence.

A schlieren study of combustion in a rapid compression machine simulating the spark ignition engine

A rapid compression machine in a configuration to simulate a spark ignition engine with a simple cylindrical combustion chamber was operated to generate high-speed schlieren movies of combustion of a propane-air mixture over a range of flow conditions. These included the flows produced by the piston alone, and by intake processes with both shrouded and nonshrouded valves. Hot-wire anemometer measurements of turbulence were made at several locations in the chamber and for two wire orientations in order to examine homogeneity and isotropy. The behavior of these flows is discussed. Burning velocity was calculated from the flame propagation velocity observed from the film and pressure records of combustion following the method of Fiock and King. For combustion with no intake generated flow, a “roll-up vortex” along the cylinder walls was observed which appeared to have only a minor influence on the flame. The burning velocity for flames produced with swirl using the shrouded valve, correlates to the intensity of turbulence according to the relations observed by Abdel-Gayed and Bradley 2 where the ratio of turbulent to laminar flame speed and the ratio of turbulent intensity to laminar flame speed are the correlation parameters. Burning velocity for combustion with the nonshrouded valve showed poorer correlation which was attributed to the problem of interpreting the hot-wire signal when no well-defined mean flow exists. The results suggest that a deficiency in the heat release for the first part of the flame travel yields a propagation velocity lower than would be expected for the extent of the observed flame. The source of this deficiency appears to be one or more of the following: o a. Incomplete reaction in the flame front. b. Finite flame thickness c. Deviations from spherical propagation as the flame and expansion flows interact with the chamber walls.