Compound steam engine — crank arrangement identification Name the compound engine in which the piston rods of the high-pressure and low-pressure cylinders are attached to two different cranks set at 90° to each other.

Introduction / Context:
Compound engines divide expansion between cylinders to improve efficiency and reduce thermal stresses. The mechanical arrangement of cranks and presence of a receiver distinguish major types. Correctly naming the configuration from a brief description is a common exam task.

Given Data / Assumptions:

• Two separate cranks set at 90° (quadrature) on the same shaft.
• Separate HP and LP cylinders delivering power out of phase.
• Receiver present between cylinders to store/transfer steam.

Concept / Approach:
In a receiver type compound engine, HP exhaust flows into an intermediate receiver before admission to the LP cylinder. Each cylinder has its own crank, typically at 90°, providing smoother torque. In a tandem compound engine, both pistons are on a common rod and act on the same crank. In the Woolf (non-receiver) type, HP exhaust goes directly to the LP cylinder without an intermediate receiver, often with both pistons sharing a rod/crank.

Step-by-Step Solution:

Verification / Alternative check:
Historical marine and mill engines used 90° receiver compounds to reduce dead-center issues and smooth torque delivery, confirming the terminology.

Why Other Options Are Wrong:

• Tandem: shares a single crank; not two cranks at 90°.
• Woolf: typically direct (non-receiver) transfer; often common rod/crank.
• Both (a) and (b): mutually exclusive configurations.

Common Pitfalls:
Confusing “receiver vs Woolf” with “tandem vs cross-compound”; mixing mechanical layout (crank count) with thermodynamic path (receiver presence).

Final Answer: