ISO 8178-7:2015

Overview

ISO 8178-7:2015 defines the parameters and procedures used to determine which reciprocating internal combustion engines may be grouped into an engine family and how to select the parent engine for emissions testing. The part applies to non-road engines for land, rail traction and marine use (excluding on-road vehicles) and supports manufacturers and approval authorities in reducing the number of engines that require full emissions testing while ensuring compliance with emission limits.

Key Topics

• Scope and responsibilities: The manufacturer identifies candidate engines, proposes family membership and provides technical justification. Parties involved (manufacturer and approval authority) agree the final family and parent-engine selection.
• Parameters defining an engine family: Basic characteristics that must be common to family members include:
  • Combustion cycle (two-stroke, four-stroke, rotary, etc.)
  • Main cooling medium (air, water, oil)
  • Individual cylinder displacement: for unit displacement ≥ 0.75 dm3, members shall be within 85%–100% of the largest; for < 0.75 dm3, within 70%–100% (unless otherwise agreed)
  • Number of cylinders (spark-ignition engines), cylinder configuration and bore centre-to-centre dimensions
  • Method of air aspiration (naturally aspirated, pressure charged, charge-cooled)
  • Fuel type (diesel, petrol, CNG/LNG, LPG, alcohols, etc.)
  • Combustion chamber type, valve/porting configuration, number of valves
  • Fuel supply type (pump-line-injector, common-rail, unit injector, carburettor, gas valve, etc.)
  • Miscellaneous features: EGR, water emulsion/injection, air injection, dual fuel, ignition type
  • Electronic control strategy: presence/absence of an ECU is a basic parameter; grouping requires technical evidence when engines are electronically controlled
  • Exhaust after-treatment systems: catalysts, DeNOx systems, particulate traps and combinations thereof
• Special cases: Interaction between parameters (e.g., cylinder count vs. aspiration or fuel system) or unlisted features with strong emissions influence must be identified by the manufacturer and may necessitate separate families.
• Parent engine selection: Three accepted methods are described:
  • Compression ignition: primary criterion is highest fuel delivery per stroke at declared maximum torque speed (secondary: highest fuel delivery per stroke at rated speed)
  • Positive ignition: primary criterion is largest displacement; tiebreakers include fuel delivery at rated power speed, most advanced spark timing and lowest EGR rate
  • Alternative method: select the engine with features known to make low emissions more difficult (detailed technical knowledge required)

Applications

ISO 8178-7:2015 is applied to non-road engine types such as:

• Agricultural and forestry equipment
• Road construction and earth-moving machines
• Industrial trucks and generating sets
• Rail traction and marine propulsion

Practical benefits include reduced testing scope and cost, clearer criteria for certification and conformity, and improved regulatory harmonization.

Related Standards

• ISO 8178 (other parts): test-bed measurement (Part 1), field measurement (Part 2), definitions and smoke measurement (Part 3), test cycles (Part 4), test fuels (Part 5), reporting (Part 6), engine group determination (Part 8), and transient procedures (Parts 9 and 10).
• Applicable national and regional non-road engine emissions regulations that reference ISO 8178 family and approval concepts.

Note: Manufacturers should engage early with approval authorities to agree engine-family boundaries and the parent-engine selection method to ensure cost-effective and defensible compliance.