The relationship between power, torque, and speed for non-road diesel engines

The relationship between power, torque, and speed for non-road diesel engines is governed by the following formula, established under ISO 15550.

### The Standard Formula

The relationship is defined by the equation for mechanical power:

P = (T × N) / 9,550

Where: P = Power (kW) | T = Torque (N·m) | N = Rotational speed (rpm)

This equation is derived from P (kW) = T (N·m) × ω (rad/s) and ω = (2 × π × N) / 60. The constant 9,550 (calculated as 60 × 1000 / (2π)) is used for unit conversion. For net power, ISO 1585 and ISO 2534 reference this framework.

### Example Calculation: 20 kW @ 3600 rpm

For a 20 kW engine at 3600 rpm, the torque is calculated as:

T (N·m) = (20 × 9550) / 3600 ≈ 53.06 N·m

This means the 20 kW engine generates approximately 53.1 N·m of torque at that specific speed, which is typical for a small air-cooled diesel unit.

### ⚙️ Relevant ISO Standards for Non-Road Engines

* ISO 15550: Establishes standard reference conditions and measurement methods for power declaration.

* ISO 14396: Specifies additional requirements for power determination during ISO 8178 exhaust emission tests.

* ISO 3046-1: Outlines power declaration, consumption, and test methods for engines in land, rail, and marine applications.

* ISO 1585 & ISO 2534: Cover engine testing for automotive vehicles, often adapted as the basis for non-road standards.