Spark advance

The distinctions between the two procedures RON and MON concern essentially the engine speed, temperature of admission and spark advance. See Table 5.8. 

Spark advance for motor method is a function of compression ratio. 

When ethanol is used in a standard spark ignition or compression ignition engine designed to bum conventional hydrocarbon-based fuels, ethanol performance varies substantially if no engine modifications are made, and it becomes difficult to rate the value of ethanol as an effective fuel. Consequently, flexible fueled vehicles (FFVs) or variable fueled vehicles (VFVs) have been developed to operate on either gasoline or alcohol-based fuels. These vehicles are equipped with on-board sensors and controls to adjust the spark advance and the fuel injector timing to help correct for the differences in fuel performance. 

A knock which is recurrent and repeatable in terms of audibility. It is controllable by the spark advance advancing the spark increases the knock intensity and retarding the spark reduces the intensity. This definition does not include surface-ignition induced knock. 

Knocking Surface Ignition Knock which has been preceded by surface ignition. It is not controllable by spark advance. It may or may not be recurrent and repeatable. 

The heart of the FFV design is a special sensor located in the fuel line between the fuel tank and the engine. This sensor instantaneously (under 50 milliseconds) determines the concentration of methanol (and/or ethanol) in the fuel. This information is fed to the engine computer which calculates appropriate spark advance and the pulse width of the fuel injector signal for correct fuel volume. Figure 1-2 illustrates the differences in Ford s 1996 Ford Taurus FFV compared to gasoline versions of their Taurus. Ford has built this FFV in models optimized for M85 and for E855. 

Fig. 7.19. Use of five-step parrot model, in conjunction with engine model, in post-processing of end gas reactions to show the influence of spark advance on autoignition. Values of pressure, temperature, mass fraction burned, and chain carrier mole fraction, C, computed from engine cycle model without end gas chemistry (broken curves) and with end gas chemistry (full curves). Spark advance before top centre with 90 octane number fuel (a) 10°, non-autoigniting cycle, (b) 20°, autoignition indicated by asterisk.

The crank angle in degrees expresses the minimum spark advance for best torque (MBT). Maximum engine torque is expressed where the spark timing is at the MBT point. Likewise, the specific fuel consumption will be at a minimum at the MBT point. 

Retarding spark to raise catalyst gas-in temperature does not deactivate the catalyst in the same way as a caUbration with optimised Speed, Load, and Spark advance parameters for the higher temperature. 

McCabe, J. C. Higher Costs Spark Advances in Process Steam and Power,... 

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