The Physics
Factbook
An encyclopedia of scientific essays

# Voltage of Automobile Spark Plugs

Bibliographic Entry Result
(w/surrounding text)
Standardized
Result
Zitzewitz, Paul & Neff, Robert. Physics. New York: Glencoe/McGraw-Hill, 1995: 482. "In your car, voltage as high as 35,000 volts is used in spark plugs and currents as large as 300 amperes are needed to turn the starter motor." 35 kV
Kim, Beverly Rae. "Automobiles." World Book Encyclopedia. New York: World Book, 1987: 936. "High voltage from 15,000 volts to 20,000 volts is needed to make the spark." 15–20 kV
Gaston, Jim. When there is no Mechanic: A General Guide to Driving Maintenance and Car Repair. United States Publishers, 1992: 102. "It boosts the low voltage in the battery from 12 volts to around 20,000 volts. This high voltage is needed to jump the gap on the spark plugs." 20 kV
Glenn, Harold T. Auto Mechanics. Peoria, Illinois: Chas. A. Bennett, 1962: 248. "Its high turn ratio develops about 20,000 volts, enough to jump the spark plug gap with ease." 20 kV
Compton's Multimedia Encyclopedia. "Automobile."CD-ROM. 1998. "The spark is caused by a momentary surge of high voltage, which may reach 20,000 volts to 25,000 volts." 20–25 kV

All automobiles have and need an ignition system. Generally all ignitions systems contain the same components, such as a battery, a distributor, and spark plugs. The battery contains the stored electrical energy, which is needed to start any automobile. After the battery releases this energy, it travels to the induction coil. The induction coil raises the voltage to a level that will be able to produce a spark in the spark plugs. Then the electricity travels to the distributor, which distributes the current to the cylinders. Each cylinder has at least one spark plug and also has a piston. The electricity forms a spark at the spark plug that ignites the gas and air mixture within each cylinder.

In a synthesis of my research findings, I discovered that automobile spark plugs do not all have a set voltage. In the sources that I used, I found that the voltage needed ranges from 15,000 to 35,000 volts. Some spark plugs require a higher or lower voltage than others.

Denise Lai -- 1999

Bibliographic Entry Result
(w/surrounding text)
Standardized
Result
Roth, Alfred C. Small Gas Engines. South Holland, IL: GoodHeart Willcox, 1975: 85. "Usually, the amount required to jump the gap is between 6,000 and 20,000 volts" 6–20 kV
Encyclopedia Americana. 15th ed. Danbury, CT: Grolier, 1996: 287. "It changes the 6 to 12 volts of the primary current into the 10,000 to 20,000 volts required to discharge at the spark plug gap" 10–20 kV
Halderman, James D. and Ellinger, Herbert E. Automotive Engines. 3rd ed. Upper Saddle River, NY: Prentice Hall, 1997: 40. "When the primary coil winding ground return path connection is "open,"the magnetic field collapses and induces a high voltage (20,000-40,000 volts)" 20–40 kV
Consoliver, Earl L, & Mitchell, Grover I. Automotive Ignition Systems. 1st ed. New York: McGraw Hill, 1920: 60. "Voltage required to jump the gap of the spark plug points, when properly adjusted, is approximately 6,000 volts" 6 kV
Bordoff, Fred. The Ignition System. Family Car (The Dream and the Reality). "… first to create a voltage high enough (20,000+) to arc across the gap of a spark plug." 20 kV
"… the voltage is stepped up from 12 volts to as much as 40,000 volts" 40 kV

The primary purpose of the ignition system, of a small gasoline engine is to provide sufficient electrical voltage to discharge a spark between the electrodes of the spark plugs. Secondly, the spark must occur at exactly the right time to ignite the highly compressed air-fuel mixture in the combustion chamber of the engine.

The ignition system must be capable of producing as much as 40,000 volts to force the electrical current across the spark plug gap. Then the intense heat created by the electrons jumping the gap ignites the air-fuel mixture surrounding the electrodes. The actual amount of voltage required depends upon variables such as compression, engine speed, shape and condition of electrodes, spark plug gap, etc.

The rate, or times per minute, at which the spark must be delivered is very high. "For example, a single cylinder, four cycle engine operating at 3600 rpm requires 1800 ignition sparks per minute. A two cycle engine running at the same speed requires 3600 sparks per minute. In multi-cylinder engines, the number of sparks per minute is multiplied by the number of cylinders".

Every spark must take place when the piston is at exactly the right place in the cylinder and during the correct stroke of the power cycle. Considering the high voltage required, the precise degree of timing and the high rate of discharges, the ignition system has a remarkable job to do

Philip Ng -- 1999