3. Additional Sensors for Combustion Analysis

In addition to in-cylinder pressure sensor, the other sensors are typically required for analyzing the processes involved during engine combustion cycle. For engine combustion diagnostics, the measurement of dynamic signals from engine subsystems (whose activity directly relates to the combustion and in-cylinder processes) is required. These subsystems also need high-speed, crank angle-based measurements to analyze their operation and effectiveness because it directly influences the engine combustion process. The most commonly measured signals for combustion analysis are low-pressure signals from intake and exhaust manifold, injection-related signals (injector needle lift, dynamic fuel pressure), temperature, mass flow, ignition-related signals (ignition timing signal, ion current signal), valve motion events, and oxygen signal for air-fuel ratio control. The present chapter deals with these additional sensors required for the combustion analysis and describes their function, mounting, and signal generation. Intake and exhaust pressure sensors are particularly important for measuring the gas exchange or low-pressure phase of the engine combustion cycle. These measurements are used in conjunction with valve lift and high-pressure cylinder measurement to derive accurate heat release calculations. Needle lift and line pressures establish the fuel injection rate and the dynamic behavior of fuel in the high-pressure fuel system at different engine operating conditions. A common requirement is to measure and evaluate the behavior of gas flow into the engine cylinder for detailed combustion analysis. Additionally, these measurements can provide data for engine simulation models that calculate cylinder residual charge and trapping efficiencies. Ignition signals are measured to relate the ignition and combustion events in spark ignition engines. The timing of the ignition of the fuel-air mixture is critical to achieve the efficient engine operation. Air-fuel ratio control is required to maintain the stoichiometric air-fuel ratio in conventional spark ignition engines. Chemical sensors are used for oxygen detection and air-fuel ratio control. Thus, the chapter describes these additional sensors required for engine combustion diagnosis.