Engine Governing Methods – Which Applies to Spark-Ignition Engines? Spark-ignition engines are primarily governed by which of the following methods under traditional control systems?

Introduction / Context:
Governing methods describe how an engine’s output is regulated. Historically, gas-fuelled and early carburetted spark-ignition engines have used different strategies from diesels because fuel and air are premixed before entering the cylinder. Understanding the classic textbook distinction clarifies multiple-choice questions that contrast SI and CI control philosophies.

Given Data / Assumptions:

• Conventional SI engines with carburetion or gaseous fuel mixers.
• No electronic fuel injection strategies considered for the basic definition.
• Comparative framing versus diesel governing (quantitative).

Concept / Approach:

In classic terminology, SI engines are said to employ qualitative governing, in which the mixture quality (fuel–air ratio) is varied to control power while the charge quantity per cycle is approximately maintained. By contrast, diesels employ quantitative governing by changing the amount of fuel injected into roughly constant air mass. Although modern throttle-based SI systems also vary charge quantity, the conventional exam answer associates SI with qualitative governing and CI with quantitative governing.

Step-by-Step Solution:

Verification / Alternative check:

Historic governing mechanisms on gas engines varied fuel admission relative to air, changing mixture richness while keeping volume similar, illustrating qualitative governing.

Why Other Options Are Wrong:

Hit-and-miss is associated with early small engines that skip firing cycles. Pure quantitative governing characterizes diesel engines. A combination can occur in modern systems but is not the standard textbook association sought here.

Common Pitfalls:

Projecting modern electronic throttle control onto historical definitions and missing the conventional exam pairing SI–qualitative versus CI–quantitative.

Final Answer:

qualitative governing (varying mixture strength at nearly constant quantity)