Modifications in CFR Engine in Order to Measure Overall Burning Time 2010-36-0119
Empirical rules for relating location of peak cylinder pressure to ignition advance at Maximum Break Torque (MBT) may be used to optimize either engines or fuel. Understanding the influences of several variables on overall burning time is possible by resorting to suitable instrument and data acquisition systems, non-standard on Cooperative Fuel Research engines (CFR engines). This work describes general aspects of the CFR engine instrument set updating aiming at reducing operator influence on measurement results, while also allowing overall burning time measurement and assessment of correlated variables influencing the combustion duration. A programmable Electronic Control Unit (ECU) operating under closed loop conditions, digital temperature controllers and a data acquisition system were retrofitted on a CFR engine. In order to evaluate the variables influencing the CFR engine combustion duration, it was necessary both to perform modifications on the control and fuel supply systems and to install complementary sensors, devices and a man-machine interface (MMI). These modifications further allow varying the relative air-fuel ratio (λ lambda), as well as the intake air and air-fuel mixture temperatures, oil temperature, fuel injection phase and pressure, and spark advance within wide limits in a controllable way. Thus, establishing the influence of these variables on overall burning time becomes possible. For the purpose of this paper and using the modifications and performed measures, the combustion duration limits were found to be from 5 to 6.2 ms, corresponding to the mean combustion speed from 12 to 16 m/s, about 33 times the laminar flame speed of most hydrocarbons at 1 bar, 25°C and stoichiometric air-fuel ratio.