ISO 8178-5-2021 pdf download.Reciprocating internal combustion engines – Exhaust emission m easurem ent t 一 Part 5: Test fuels.
5.3 Influence of fuel properties on emissions from spark ignition (SI) engines
Fuel parameters that have a significant influence on emissions and fuel consumption of an SI engine include octane number, sulfur level, metal-containing additives, oxygenates, olefins and benzene.
Engines are designed and calibrated for a certain octane value or methane number. When a customer uses gasoline with an octane level lower than that required, or accordingly, a natural gas with a lower methane number, knocking can result which could lead to severe engine damage. Engines equipped with knock sensors can handle lower octane or methane number levels by retarding the spark timing.
As mentioned above, sulfur naturally occurs in crude oil. If the sulfur is not removed during the refining process, it will contaminate the fuel. Sulfur has a significant impact on engine emissions by reducing the efficiency of catalysts. Sulfur also adversely affects heated exhaust gas oxygen sensors. Consequently, high sulfur levels will significantly increase HC and NO emissions. Also, lean burn technologies, which require NO aftertreatment technologies, are extremely sensitive to sulfur.
Metal-containing additives usually form ash and can therefore adversely affect the operation of catalysts and other components, such as oxygen sensors, in an irreversible way that increases emissions. For example, MMT (methylcyclopentadienyl manganese tricarbonyl) is a manganese-based compound marketed as an octane-enhancing fuel additive for gasoline. The combustion products of MMT coat internal engine components, such as spark plugs, can potentially cause misfire which leads to increased emissions, increased fuel consumption and poor engine performance. They also accumulate and partly plug the catalyst causing an increased fuel consumption in addition to reduced emission control.
Oxygenated organic compounds, such as ethanol, are often added to gasoline to increase octane, to extend gasoline supplies, or to induce a lean shift in engine stoichiometry to reduce carbon monoxide emissions. The leaner operation reduces carbon monoxide emissions, especially with carbureted engines without electronic feedback-controlled fuel systems. However increased 02 levels beyond that for which an open loop engine has been calibrated will typically increase N0 emissions and combustion temperatures which can lead to premature engine failure.
Olefins are unsaturated hydrocarbons and, in many cases, are also good octane components of gasoline.
However, olefins in gasoline can lead to gum and deposit formation and increased emissions of reactive
(i.e. ozone-forming) hydrocarbons and toxic compounds.
Benzene is a naturally occurring constituent of crude oil and is also a product of catalytic reforming that produces high octane gasoline streams. It is also a known human carcinogen. The control of benzene levels in gasoline is the most direct way to limit evaporative and exhaust emissions of benzene from SI engines.
Proper volatility of gasoline is critical to the operation of SI engines with respect to both performance and emissions. Volatility is characterized by two measurements, vapour pressure and distillation.ISO 8178-5 pdf download