Octane Number The Scale for Gasoline Antiknock Quality

Octane Number; The Scale for Gasoline Anti-knock Quality Buland I. Dizayi Ph. D Salahaddin University

Test Principle • The tested fuel is assigned a number based on the highest useful compression ratio (HUCR). • The scale is based on the knock resistivity of various blends of two standard fuels having the same major properties except their octane number. Salahaddin University

Octane Scale • Iso-octane (2, 2, 4 trimethylpentane) and • n-heptane are the chosen standard fuels. Salahaddin University

Test Procedure Research Octane Number (RON) and Motor Octane Number(MON) RON is more likely related to low speed and mild driving conditions. MON is related to high speed severe driving conditions due to: • Improvements in engine design. • The propensity to a more aggressive driving behavior. Salahaddin University

RON and MON test conditions. Salahaddin University

Road Octane Number • Salahaddin University

Different Scales across the world • Salahaddin University

Fuel behavior under different operational conditions • Direct fuel injection engines (GDI) and turbo-charged engines (TSI) might work at a severity lower than RON as in (C 1). • Others might work beyond MON which is relatively harsh operation such as two-stroke engines as in (C 2). Salahaddin University

Gasoline components Octane quality distribution • Most of gasolines behave like fuel (A) which is characterized by low RON for the light (low boiling point) components and high RON for the heavier (high boiling point) components. • The components of fuel (B) possess almost the same RON. Salahaddin University

Octane Index and Modern Engines • Salahaddin University

Shrinking of MON contribution The reliability of MON is decreasing especially in the EU due to: • The lower in-cylinder pressure of the MON test due to low volumetric efficiency. • A high-power output from the engine is obtained from the higher mean effective pressure (mep) at low temperatures to avoid knock. These are the conditions for RON. Salahaddin University

Salahaddin University

Reliability of RON Salahaddin University

The influence of fuel chemical structure on the octane quality (Branching) Salahaddin University

The influence of fuel chemical structure on the octane quality (Saturation) Salahaddin University

Octane Requirement Increase (ORI) • OR increases with vehicle ageing due to the combustion chamber deposits (CCD). • New engines after accumulating several thousands of kilometers could have ORI in the range of 2~10 numbers. Salahaddin University

The way CCD affect the ORI • 90% of ORI is due to thermal insulation of the CCD which will increase the combustion chamber temperature and hence the endgas. • 10% of ORI is due to the increase of compression ratio as the CCD build-up, and the catalytic nature of the deposits to accelerate the pre-flame reactions. Salahaddin University