Fuel Comparison

Features

SP98 (Super Fuel 98)

AVGAS 100LL (Aviation Gasoline 100 Low Lead)

Ethanol E85

Motor Octane Number (MON)

88-90

99-100

100 - 105

Research Octane Number

100-106

104-108

Density (at 15°C, kg/m³)

720-780

720-750

760-810

Vapor lock temperature

50°C

70°C

80°C

Freezing temperature

Approximately 60°C

Approximately -58°C

-70°C

Ice formation temperature

-5°C

-30°C

Solubility in water

Insoluble

Miscible

Detonation power

Low (high octane rating)

Very low (designed for aircraft engines)

Very low (high resistance to knocking)

Environmental Impact

Emits greenhouse gases and pollutants

Significant toxic emissions, including lead

Very strong reduction in CO2 emissions to completely neutral, depending on the source of the ethanol.

Formulation stop date

N/A (still evolving)

Fixed in 1972

N/A (evolves to reduce pollutants)

Common Use

Road vehicles

Light aircraft with piston engines

Flex-fuel vehicles, automotive racing

Average price (2024 reference, €/L)

2.10€

3.20€

0.80€

Boiling/Evaporation Temperature

25 - 210°C (varies according to the season and ethanol content)

38 - 170°C (varies according to components)

78°C (pure ethanol)

Auto-ignition temperature

280-300°C

~ 210°C

365°C (pure ethanol)

Vapor pressure (at 37.8°C, kPa)

45-60 kPa

38-49 kPa

45-105 kPa (varies according to the season and ethanol content)

Viscosity (at 20°C, mm²/s)

0.6-0.8 mm²/s

~ 0.65 mm²/s

~ 1.2 mm²/s (varies according to the season and ethanol content)

Lower Heating Value (LHV, MJ/kg)

42-43 MJ/kg

44 MJ/kg

26-28 MJ/kg

Energy density (MJ/kg)

44-46 MJ/kg

43-44 MJ/kg

~ 30 MJ/kg (varies according to the season and ethanol contentl)

Toxic compound content

Aromatic hydrocarbons, benzene (<1%) (<1%)

Tetraethyllead, benzene

Traces of ethanolamine, low benzene content

Standard governing the composition

EN 228

ASTM D910

EN 15293 (Europe), ASTM D5798 (États-Unis)

Tests conducted by independent laboratories - PDF for consultation

Aging test of fuel hoses in SP98 and E85 - Download

European Standard E85 - Download

Super Plus Unleaded Gasoline 98 - BAS EN 228 - Download

Vapor Pressure Definition

Vapor pressure: The vapor pressure of a liquid is the pressure exerted by the vapor of the liquid when it is in equilibrium with its liquid phase at a given temperature. The higher the vapor pressure, the more the liquid tends to evaporate quickly. In practical terms, this means that fuels with higher vapor pressure are more volatile and can evaporate more easily, which can influence cold start performance and emissions of volatile organic compounds (VOCs). For example, ethanol has a vapor pressure that varies significantly depending on the proportion in the mixture, which affects its behavior under different climatic conditions.

Factors Influencing Consumption with E85

1. Lower Heating Value (LHV): The LHV of E85 is indeed lower than that of SP98, which means that, at equal volume, E85 contains less energy. This is the main reason why there is an increase in consumption. However, this increase in consumption is not strictly proportional to the difference in LHV, due to the following factors.

2. Mixture richness and stoichiometric combustion: E85 allows operation with leaner mixtures (closer to the stoichiometric ratio, which is 9.7:1 for E85 compared to 14.7:1 for SP98). This ability to operate with a leaner mixture can partially offset the lower energy density of the fuel, thereby reducing potential overconsumption.

3. Cooling effect of intake air: E85 has a high capacity to absorb heat during evaporation, which cools the intake air. Cooler air is denser, containing more oxygen, which allows for better combustion. This cooling also improves the volumetric efficiency of the engine, contributing to better performance and, in some cases, a reduction in fuel consumption.

4. Knock resistance and ignition optimization: E85 has a higher octane rating, allowing for increased ignition timing and reduced knocking. It also enables higher compression, which increases the engine's thermodynamic efficiency. This ability to optimize engine settings allows for more power to be extracted from each combustion cycle.

Refined estimation of overconsumption

- Overconsumption: Instead of basing overconsumption solely on the difference in PCI, by considering the advantages of E85 (better stoichiometric combustion, intake air cooling, ignition optimization), overconsumption is generally observed in a range of 15% to 25% in engines optimized for E85, compared to SP98.

Conclusion

The overconsumption with E85 compared to SP98 is therefore not strictly related to the difference in calorific value, but is mitigated by the fuel's advantages in terms of mixture management, intake cooling, and improvement of ignition and compression parameters. This analysis demonstrates that in an optimized engine, the overconsumption could be lower than the figures often cited.