Effect of Gasoline Fuel Additives on Combustion and Engine Performance

Figure 3.11: Current and Voltage traces from the COP-ignition coil 
Arc phase follows with lower voltage and current characteristics. The added 
energy applied to the spark gap during the breakdown phase reduces the voltage 
0.0
5.0
10.0
15.0
20.0
25.0
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
-1.50
-1.00
-0.50
0.00
0.50
1.00
1.50
T
ri
gger 
Si
gnal
, 
V
 /
 Spark
 C
urrent
, 
m
A
Spark
 V
ol
tage, k
V
Time, ms
Voltage
Signal
Current
t1
t2
t3 

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3.2 Combustion Experiments 
87 
required to maintain the arc from >2-3 kV to typically around 100-200 V. Due to 
increased timescales involved in this phase, the total energy released is greater, 
although peak power output is reduced. In the final, glow phase, of the spark discharge, 
power output reduces further still due to the finite nature of energy stored. This results 
in fewer molecules being ionised and less current being carried. Consequently, an 
increase in voltage is often experienced. This phase lasts until no more ionised gas 
molecules are available and current stops flowing, represented by t
3 
in Figure 3.11. As 
mentioned previously, spark occurs when measured current is positive which is 
defined as the time interval from t
2
to t
3
. 
Figure 3.12: End of spark signal to beginning of spark delay. Dwell time 0.8 ms. 
Figure 3.12 displays typical delays from end of spark signal to start of spark at 
0.8 ms dwell time. The spark-to-spark average delay was measured as 238.75 µs with 
a standard deviation of 0.81 %. The delay could be shortened with longer dwell time 
due to higher potential differences being achieved in the electrode gap as a result of 
larger magnetic field being created between primary and secondary windings of the 
ignition coil.