Measuring indicated power (multi-cylinder SI engine) Which test method is commonly used to determine the indicated power of a multi-cylinder spark-ignition engine?

Introduction / Context:
Indicated power (IP) quantifies the net work developed in the cylinders. Direct measurement on multi-cylinder engines is difficult without cylinder pressure indicating equipment. The Morse test offers a practical alternative to estimate IP from accessible brake measurements by cutting out cylinders sequentially.

Given Data / Assumptions:

• Multi-cylinder spark-ignition engine operating at constant speed.
• Ability to disable cylinders one at a time (e.g., shorting spark plugs).
• Brake power measured on a dynamometer.

Concept / Approach:

The Morse test estimates the indicated power of each cylinder by observing the drop in brake power when that cylinder is cut out. Summing the per-cylinder indicated contributions gives total IP. Since BP is measured directly, and losses are assumed nearly unchanged at constant speed, the differences yield a reasonable IP estimate without in-cylinder pressure transducers.

Step-by-Step Solution:

Verification / Alternative check:

Comparisons with indicated diagrams show acceptable accuracy for tuning and diagnostics, though precision studies still prefer pressure-indicating equipment.

Why Other Options Are Wrong:

Prony brake test measures BP, not IP. Motoring test assesses friction power by driving the engine. Heat balance test partitions energy flows but does not directly yield IP. Willans line uses fuel flow versus power for efficiency mapping, not IP per se.

Common Pitfalls:

Assuming friction and pumping losses remain perfectly constant; slight variations can introduce error, so results are approximate.

Final Answer:

Morse test