Two technicians are discussing the design of a waste spark ignition system. Technician A says that the polarity of a waste spark coil is reversed each time it fires so that the negatively firing spark plug always ignites an air/ fuel charge. Technician B says that a waste spark coil may be mounted directly on top of one of the spark plugs that it fires. Who is correct?
A. Technician A only
B. Technician B only
C. Both technicians
D. Neither technician
The correct answer and explanation is:
Correct Answer: B. Technician B only
Explanation:
Technician A’s statement: Technician A is incorrect. In a waste spark ignition system, the polarity of a waste spark coil does not reverse each time it fires. The system works by firing two spark plugs simultaneously, with one spark occurring in the cylinder that is on its compression stroke (igniting the air-fuel mixture) and the other spark occurring in the cylinder that is on its exhaust stroke (the “waste” spark). The polarity of the spark is fixed because each end of the coil has a designated polarity (one positive and one negative). One spark plug fires with a positive polarity (electrons flowing from the center electrode to the ground electrode), and the other fires with a negative polarity (electrons flowing from the ground electrode to the center electrode). This polarity remains consistent and does not reverse during operation.
Technician B’s statement: Technician B is correct. In some waste spark ignition systems, the coil pack is designed so that it can be mounted directly on top of one of the spark plugs it fires. This configuration is commonly referred to as a “coil-on-plug” design. It eliminates the need for high-voltage spark plug wires for that particular spark plug, thereby reducing electrical losses and increasing reliability. However, the waste spark coil will still fire two spark plugs simultaneously, with the second spark plug connected via a wire or another mechanism.
Conclusion: While Technician A’s understanding of polarity in waste spark systems is incorrect, Technician B accurately describes a design feature of some waste spark systems. Therefore, the correct answer is B. Technician B only.