Combustion control is one of the keys to obtain better performance and pollutants emission, both for diesel, spark ignition and HCCI engines. This paper presents a low-cost and high performance system based on commercially available hardware and software, which allows the implementation of control and diagnostic strategies based on combustions analysis, with the typical Rapid Control Prototyping (RCP) advantages (user friendly development tools, real time calibration, etc.).
Information on the combustion process can be accessed by means of an indicating sensor such as an in-cylinder pressure transducer, or a ionization current measurement system, depending on the application. The signal must be sampled with a fast sampling system within a given crank angle window. It is then possible to process the input signal, in order to evaluate diagnostic or control indexes which can be calculated before the end of the same engine cycle, and finally used to correct the engine control parameters.
A knock detection strategy for engine mapping applications has been defined and implemented on the system. Standard equipment Variable Reluctance Sensors (VRS) were used for crankshaft and camshaft position detection, while both in-cylinder pressure sensors and accelerometers were considered as knock sensitive signals. The crankshaft and camshaft position signals are necessary for the windowing task, limiting the analysis of knock related signals to a precise portion of the engine cycle. Many different techniques have been compared, in order to find out whether it is possible to define an index whose critical (knocking) values are independent of the engine operating range (and hopefully independent of the engine characteristics).
The system proved to be efficient, being able to analyze up to 4 signals at a time, over different windows: there aren't limitations on the windows position and dimension nor on the engine speed.
The same system can be used for other purposes, such as 50% Mass Fuel Burned (MFB) crank angle determination, or heat release analysis for combustion control in diesel or Homogeneous Charge Compression Ignition (HCCI) engines.