Fuel Injector Flow Rate Calculator

How to Calculate Fuel Injector Flow Rate

Calculating the fuel injector flow rate is crucial for optimizing engine performance. This calculation takes into account factors such as target horsepower, number of cylinders, fuel pressure, aspiration type, and duty cycle.

What is the Formula?

The formula for calculating fuel injector flow rate is:

\[ Flow Rate (lb/hr) = \frac{Horsepower \times BSFC}{Number of Cylinders \times (Duty Cycle / 100)} \]

Where:

• Flow Rate is in pounds per hour (lb/hr)
• Horsepower is the target engine horsepower
• BSFC is the Brake Specific Fuel Consumption (typically 0.55 for naturally aspirated engines, 0.65 for forced induction)
• Number of Cylinders is the engine's cylinder count
• Duty Cycle is the maximum injector duty cycle (typically 80-85%)

To convert the flow rate to cc/min, multiply the result by 10.5:

\[ Flow Rate (cc/min) = Flow Rate (lb/hr) \times 10.5 \]

What are the calculation steps?

1. Determine the target horsepower of the engine.
2. Identify the number of cylinders in the engine.
3. Determine the BSFC based on the engine's aspiration type.
4. Set the maximum duty cycle (typically 80-85%).
5. Apply the formula to calculate the flow rate in lb/hr.
6. Convert the result to cc/min by multiplying by 10.5.

Example Calculation

Let's calculate the fuel injector flow rate for an engine with the following parameters:

• Target Horsepower: 400 hp
• Number of Cylinders: 8
• Aspiration: Naturally aspirated (BSFC = 0.55)
• Duty Cycle: 85%

Step 1: Apply the formula for lb/hr

\[ Flow Rate (lb/hr) = \frac{400 \times 0.55}{8 \times (85 / 100)} = 32.35 lb/hr \]

Step 2: Convert to cc/min

\[ Flow Rate (cc/min) = 32.35 \times 10.5 = 339.68 cc/min \]

Therefore, the recommended fuel injector flow rate for this engine is approximately 32.35 lb/hr or 339.68 cc/min.

Diagram of Fuel Injector Flow Rate Calculation

The following diagram illustrates the concept of fuel injector flow rate calculation:

This diagram shows the relationship between the flow rate in lb/hr and cc/min. The height of each bar represents the calculated flow rate, providing a visual comparison between the two units of measurement.