Engine testing — purpose of the Morse test The Morse test is commonly used to determine which performance parameter of an internal-combustion engine?

Introduction / Context:
The Morse test is a practical workshop method to estimate indicated power of multi-cylinder engines when direct cylinder-pressure indication is not available. It relies on measuring changes in brake power as cylinders are disabled sequentially.

Given Data / Assumptions:

• Engine with multiple cylinders and independent ignition/fuel cut-off.
• Brake dynamometer available to measure brake power.
• Speed held approximately constant during the test.

Concept / Approach:
Indicated power is not directly measured on the dynamometer. The Morse method disables one cylinder at a time, observing the drop in brake power. Assuming mechanical losses remain approximately constant at a given speed, the loss in brake power when a cylinder is cut corresponds to that cylinder’s indicated power contribution.

Step-by-Step Solution:
Measure brake power with all cylinders firing: BP_all.Disable cylinder i; measure BP_i_off.Indicated power of cylinder i ≈ BP_all − BP_i_off.Sum over cylinders to estimate total I.P.; mechanical efficiency = BP_all / IP_total.

Verification / Alternative check:
Results can be cross-checked with indicator diagrams where available or with cylinder pressure transducers on modern engines.

Why Other Options Are Wrong:
Single-cylinder (Option B) does not need Morse; direct methods are used. Brake power (Option C) is measured directly by dynamometer, not via Morse estimation. Compression ratio (Option D) is a geometric parameter, unrelated to Morse testing.

Common Pitfalls:
Allowing speed to vary significantly during disabling skews results because friction and pumping losses are speed-dependent.

Final Answer:
Indicated power (I.P.) of a multi-cylinder engine