ISO 7440-2:1991

Overview

ISO 7440-2:1991 - "Road vehicles - Fuel injection equipment testing - Part 2: Orifice plate flow‑measurement" specifies a test system and fixture for accurate flow measurement of single‑orifice plates (pastilles à trou) used in injector calibration assemblies. The standard covers orifice diameters from 0.4 mm to 0.8 mm and defines the measurement circuit, fixture geometry, reference conditions and correction procedures to ensure repeatable, traceable flow results for diesel fuel injection testing.

Key topics and technical requirements

• Scope and intended users: Primarily for manufacturers of single‑orifice nozzles and test laboratories used for injector and pump calibration.
• Test system components: A fluid feed circuit, primary flow‑measuring device (example circuit described in Annex A), a mounting fixture for the orifice plate (detailed functional dimensions shown), and an optional flow‑control/check device (Annex B).
• Reference conditions:
  • Flow volume referenced to 40 °C.
  • Reference density: 0.808 g/cm³ at 40 °C.
  • Reference dynamic viscosity: 2.1 × 10⁻³ Pa·s at 40 °C.
  • Typical inlet pressure example: 10 MPa (100 bar) with outlet at ambient.
• Measurement accuracy and control:
  • Volume flow accuracy: ±0.2% of reading at 40 °C.
  • Temperature control and measurement: tight control (±0.5 °C for calibration; inlet stability ±1 °C during measurement).
  • Pressure stability: inlet pressure tolerance ±0.01 MPa (0.1 bar) and allowable cyclic variation limits (±0.1 MPa / 1 bar).
  • The standard requires frequent monitoring of fuel viscosity and density and disposal if out of specification (fuel per ISO 4113).
• Corrections and computation: An empirical correction formula compensates for differences in temperature, density and viscosity. The standard provides orifice‑specific coefficients (K) for 0.4–0.8 mm orifices to apply these corrections.
• Annex B (informative): Describes an optional calibration/control device with master/slave chambers, a three‑way valve, level and temperature sensors, a time counter (display to 0.001 s), and detailed design/accuracy expectations.

Applications

• Calibration and acceptance testing of diesel injector nozzles and injector calibration assemblies.
• Quality control-manufacturers of orifice plates/nozzles use ISO 7440-2 to validate production.
• Engine test labs and pump/injector testing benches where accurate, traceable flow data for small orifices (0.4–0.8 mm) are required.
• Research and development for fuel injection system design and metrology.

Related standards

• ISO 7440-1:1991 - Injector calibration assemblies (complements Part 2).
• ISO 4113:1988 - Specifies test fuel and fluid requirements used with this flow measurement method.

Keywords: ISO 7440-2:1991, orifice plate flow‑measurement, fuel injection equipment testing, diesel injector testing, orifice 0.4–0.8 mm, flow measurement standard, injector calibration.