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Technical Paper

Spectrogram Analysis of Accelerometer-Based Spark Knock Detection Waveforms

Spark knock pressure oscillations can be detected by a cylinder pressure transducer or by an accelerometer mounted on the engine block. Accelerometer-based detection is lower cost but is affected by extraneous mechanical vibrations and the frequency response of the engine block and accelerometer. The knock oscillation frequency changes during the expansion stroke because the chamber geometry is changing due to the piston motion and the burned gases are cooling. Spectrogram analysis shows the time-dependent frequency content of the pressure and acceleration signals, revealing characteristic signatures of knock and mechanical vibrations. Illustrative spectrograms are presented which yield physical insight into accelerometer-based knock detection.
Technical Paper

Detection of Spark Knock Oscillations: Dependence on Combustion Temperature

The frequency of the pressure oscillations caused by spark knock depends on the temperature-dependent speed of sound in the combustion gases. Engine dynamometer tests showed a 6.5% (390 Hz) reduction in the knock fundamental frequency as the air/fuel ratio was swept from 13:1 to 20:1. Engine cycle simulation model predictions of maximum burned gas temperatures correlate well with the data. A robust knock detection system must be insensitive to the range of burned gas temperature (frequency of pressure oscillations) that will be encountered with a particular engine control system operating under the expected range of fuels and environmental conditions.
Technical Paper

A Review of the Effect of Engine Operating Conditions on Borderline Knock

The effects of engine operating conditions on the octane requirement and the resulting knock-limited output were studied on a single cylinder engine using production cylinder heads. A 4-valve cylinder head with port deactivation was used to study the effect of fuel octane, inlet air temperature, coolant temperature, air/fuel ratio, compression ratio and exhaust back pressure. The effect of the thermal environment was studied in more detail using separate cooling systems for the cylinder head and engine block on a 2-valve cylinder head. The results of this study compared closely with results found in the literature even though the engine and/or operating conditions were quite different in many cases.
Technical Paper

Measurements of the Effect of In-Cylinder Motion on Flame Development and Cycle-to-Cycle Variations Using an Ionization Probe Head Gasket

An ionization probe head gasket (to IPHG) was used to investigate flame development in a 2.0L I4 engine with two in-cylinder fluid motions. A new technique was developed to display accurate flame contours at 2%, 10% and 50% mass fraction burned crank angles using the measurements of flame arrival time from the ion probes in conjunction with cycle simulations. The flame arrival and burn rate information is used to scale the relationship between flame radius and mass fraction burned from the cycle simulation to create accurate contours of the flame for each cycle. The tumbling motion inside the combustion chamber produced by the production intake ports convected the flame towards the exhaust side of the chamber. The geometry of the flame development was relatively unaffected by changes in speed and load.
Technical Paper

The Effects of Injector Targeting and Fuel Volatility on Fuel Dynamics in a PFI Engine During Warm-up: Part II - Modeling Results

The effects of injector targeting and fuel volatility on transient fuel dynamics were studied with a comprehensive quasi-dimensional model and compared with experimental results from Part I of this report (1). The model includes the transient, convective vaporization of four multi-component fuel films coupled with a transient thermal warm-up model for realistic valve, port and cylinder temperatures (2, 3). Two injector targetings were analyzed, first with the fuel impacting the intake valve and in addition, the fuel impacting the port floor directly in front of the intake valve. The model demonstrates the importance of both component temperature and fuel impaction area on fuel vaporization, transient air fuel ratio (AFR) response and the amount of liquid fuel entering the cylinder. Generally, a smaller injector footprint area will lead to more liquid fuel entering the cylinder even if the spray is targeted at the back of the intake valve.