Spark timing

Signal from engine computer adjusts fuel flew and spark timing... 

The best efficiency attainable from a gasoline engine of specified power rating depends heavily on four parameters compression ratio, air/fuel ratio, spark timing, and the fraction of the mechanical energy developed in the cylinder or cylinders devot-... 

The quantity of NO formed in a petrol engine or diesel engine depends on the combustion parameters and, to a certain extent, can be controlled by adjustment of the engine operation. For example, NO formation may be limited by retarding the spark timing in petrol engines and the fuel injection in diesel engines [8]. 

Chemical analysis can turn up in unexpected places. Modern engines in automobiles have been made much more fuel-efficient and less polluting by the inclusion of a sensor to analyze the oxygen (02) concentration in the exhaust gases. The signal from this sensor is sent to the computer that controls engine function so that instantaneous adjustments can be made in spark timing and air-fuel mixtures. 

The original CFR test conditions appear in the second column of Table 7.2. These constitute the Research method and assign the fuel a Research octane number (RON). It was found that typical fuel susceptibility to knock in practical engines did not correlate sufficiently well with this test and one with rather more severe conditions - the Motor method, giving the Motor octane number (MON) - now also is used. These conditions are given in the third column. The inlet manifold temperature and speed have been increased, spark timing advanced, and a shrouded inlet valve fitted to... 

Spark timing, crank angle before tdc 13 14 to 26° (depends on CR)... 

S. Brussovansky, J. Heywood and J. Keck, Predicting the Effects of Air and Coolant Temperature, Deposits, Spark Timing and Speed on Knock in Spark Ignition Engines, SAE Technical Paper 922324 (1992). 

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. 

The amount of pollutants produced depends on air/fuel ratio and spark timing. When rich mixture is supplied there is not enough oxygen available to convert CO to C02. Similarly, NOx production depends on the time and temperature history of the fuel supplied. When rich gas mixtures are supplied... 

Similarly, the ethylene-based control system was used to actively control the spark timing of the NFS predetonator tube. When ethylene is detected at the tail-end, a signal is sent to actuate the ignitor ensuring full tube fills and minimizing wasted fuel. As shown in Fig. 10.9, the missing peaks in the equivalence ratio histories are due to detonation failure due to pulse-to-pulse interference. The actively controlled spark is able to reduce this performance-degrading behavior. 

Figure 10.9 Results of active control experiments at the NFS PDE facility using a 3.8-centimeter diameter, 20-centimeter-long tube running on ethylene/oxygen with a continuous air purge. The equivalence ratio at the tail-end is shown for (o) fixed spark timing (control off) and (6) actively controlled spark timing using the fuel diagnostic (control on).

Spark Time ( BTDC) Air-Fuel Ratio Ignition Delay (ms) Combustion Time (ms) Ignition Delay (ms) Combustion Time (ms)... 

Spark timing, and data collection are performed under the control of a microcomputer so that signal can be obtained from repetitive ignitions. The bomb was filled to an initial pressure of 32 kPa with mixtures of CH -02 Ar having different stoichiometries. The ratio of oxygen to argon was identical to the 02JN2 ratio in air for all but one experiment. 

Chamber geometry Spark timing Staged combustion External combustion... 

Fluctuations in the heating value of the fuel may require constant adjustment of spark timing and could also require derating of the power output capability. 

---