What is the differences between lb/hr and cc/min and mm^3 in a Fuel Injector
lb/hr, cc/min, and mm³ (cubic millimeters) are units used to express the flow rate of a fuel injector. Each has a specific system of measurement and application focus. Here’s how they differ:
- lb/hr (Pounds per Hour)
- System: Imperial (U.S. customary).
- Measurement Type: Mass flow rate (weight of fuel per time).
- Description: Measures the weight of fuel the injector delivers in one hour at a specified fuel pressure.
- Common Usage: Popular in the U.S. and for BSFC (Brake Specific Fuel Consumption) calculations, as BSFC uses fuel mass in pounds.
- Example: An injector rated at 42 lb/hr can flow 42 pounds of fuel per hour.
- 2. cc/min (Cubic Centimeters per Minute)
- System: Metric.
- Measurement Type: Volume flow rate (volume of fuel per time).
- Description: Measures the volume of fuel delivered per minute at a specified pressure.
- Common Usage: Widely used globally and often specified in manufacturers’ datasheets.
- Example: An injector rated at 450 cc/min flows 450 cubic centimeters of fuel per minute.
- 3. mm³ (Cubic Millimeters)
- System: Metric (smaller-scale unit).
- Measurement Type: Volume flow rate (volume per injection event or per time).
- Description: Typically used for high-precision measurement of fuel delivery in systems like common rail diesel injectors, where flow rates are much smaller per injection event.
- Common Usage: Common in diesel engines, where injectors operate at very high pressures and deliver small quantities of fuel with high precision.
- Conversion Factor:
- 1 cc = 1,000 mm³ (since 1 cubic centimeter = 1,000 cubic millimeters).
- For example, 450 cc/min = 450,000 mm³/min.
Key Differences
| Aspect | lb/hr | cc/min | mm³ |
|---|---|---|---|
| System of Units | Imperial | Metric | Metric |
| Type of Measurement | Mass (weight) | Volume | Volume |
| Typical Application | Gasoline engines (U.S.) | Global (gasoline and diesel) | High-precision (diesel, gasoline GDI & Piezo injectors) |
| Scale | Large-scale flow | Medium-scale flow | Small-scale, high-precision flow |
Conversion Between Units
Why Use Each Unit?
- lb/hr: Best for U.S. systems, BSFC, and horsepower calculations.
- cc/min: Standard for international injector specs and flow ratings.
- mm³: Used in diesel engines and gasoline GDI and Piezoelectric engines where high-pressure injectors deliver very small fuel quantities.
By understanding these units and their conversions, you can interpret injector specifications and performance across different systems and applications.