4. Computer-Aided Data Acquisition

Combustion diagnostic research on reciprocating engines often requires the observation and recording of rapidly changing variables such as in-cylinder pressure, diesel fuel injection pressure, diesel injector needle position, ignition current, etc. The magnitude of these variables often changes significantly in milliseconds. Typically, data needs to be recorded on a crank angle basis in engine cycle-resolved measurements, which requires a high-speed data acquisition system. The present chapter describes the general principles of data acquisition system along with the functions of its elements. Generally, in any data acquisition system, the essential sequence of operation includes input signal generation by transducers, signal conditioning, multiplexing, analog-to-digital conversion (sampling of data), and data processing. All these operations involved in data acquisition are described with a specific focus on engine combustion measurement. Typical analog and digital signals involved in engine combustion measurement along with their signal conditioning are also presented. Data sampling needs to be carried out properly to circumvent the loss of signal that can lead to misinterpretation of actual phenomena during the combustion process. This chapter describes the issues involved in the sampling of data and sampling rate requirement for different engine combustion modes and operating conditions. Additionally, offline and online processing of measured combustion data is also briefly discussed.