Automotive Fuels Flashcards
What are the four main properties important for a gasoline
- Combustion : high resistance to auto-ignition
- Volatility
- Pollution / Corrosivity (sulfur and benzene content)
- Stability
Which particular property is adjusted for each country, even in Europe ?
Specs related to volatility are adjusted depending on the climate of each country
What is one major problem that we want to avoid during combustion of automotive fuels ?
We want to avoid knocking effect due to auto-ignition
What is Knocking ?
Knocking occurs when we have uncontrolled auto-inflammation of the fuel/air mixture in different zones of the combustion chamber. It leads to overheating of the engine
What conditions favor knocking in the cylinder ?
High pressure and/or temperatures, but also poor homogeneity of the air/fuel mixture favor knocking
How can we detect knocking ?
Knocking can be detected by a characteristic metallic noise
What is the parameter measured to control auto-ignition of a gasoline blend ?
We use the octane number
What is the name of the engine that enables the calculation of the octane number ?
The octane number is measured on the CFR engine
Which molecules are the two references for the measure of the octane number ?
The two references are isoOctane (2,2,4-triméthylpentane) and n-heptane
What do RON and MON stand for
Research Octane Number and Motor Octane Number
What is the difference between RON and MON
The RON measures the octane number simulating the conditions of a cold engine while the MON measure the octane number for an engine that has been running for a while
What is the European specification for RON/MON of the two Unleaded Super and LPG fuel ?
- Unleaded Super 98 : RON 98 / MON 87
- Unleaded Super 95 : RON 95 / MON 85
- LPG Fuel : RON - / MON 89
Why do LPGs have such a high MON ?
From the PIANO table we would expect bad performance but actually, LPG are made of very small paraffins which are very stable and therefore are good to resist auto-ignition
How are US specs regarding octane number different from European ones ?
In Europe RON and MON have different specs while in the US, there is only one spec on the arithmetic mean of the two values
Why are the two main families of components of gasoline good ?
We want to avoid auto-ignition :
- aromatics are very stable
- isoparaffins are stable thanks to tertiary and quaternary carbons
How good is the RON for the main families of components ?
- nP : very low
- iP : high
- A : very high
- N : medium
- O : medium
How good is the MON for the main families of components ?
- nP : very low
- iP : very high
- A : high
- N : medium
- O : medium
What is the RON and MON for FCC gasoline ?
RON ok but low MON because of high content of olefins
Why is the MON of FCC gasoline low ?
Because of the high olefin content
How is the RON and MON of butane ?
It’s a short molecule so very stable -> good RON and MON
How is the RON and MON of reformate ?
The RON is excellent and MON ok because of high aromatic content
How is the RON and MON of alkylates ?
The RON is good and the MON is excellent because of the high isoparaffinic content
Why are alkylates very interesting nowadays for RON and MON ?
Alkylates are interesting because they enable high octane number without aromatics
What does LVN stand for ?
Light Virgin Naphtha
Where do LVN and IVN come from ?
LVN and IVN come from straight run gasoline
What should LVN contain ?
LVN should contain C5 and C6
Where is LVN sent ?
LVN is usually sent to isomerization units to produce paraffins
What should IVN contain ?
IVN should contqin C7+ molecules (to avoid benzene)
Where is IVN usually sent ?
IVN is usually sent to reforming unit
What are LCN and HCN ?
LCN is Light Cat Naphtha and HCN is Heavy Cat Naphtha
Where do LCN and HCN come from ?
They come from FCC gasoline
Why are LCN and HCN separated ?
LCN is olefin rich but not too aromatic while HCN is aromatic rich with a moderate amount of olefins
Why do we have ASTM specifications ?
ASTM enables us to check that the gasoline is homogeneous and that we will get a smooth combustion
What are the specs related to ASTM ?
We check IBP, EBP and % of gasoline distillated at 70, 100 and 150°C
Why do we check the volatility of the gasoline ?
We have a minimum spec because we need a minimum amount of vapor to start ignition and a max to avoid losses of volatile components
How is VP adjusted ?
We use butane to adjust the VP
What does DVPE stand for ?
Dry Vapor Pressure Equivalent
Why do refiners prefer to be close to the max VP spec ?
- Gasoline must remain on spec until the filling station
- Economically interesting to sell butane at the price of gasoline
What is the maximum benzene content in gasoline ?
Max 1% benzene in Europe
What are the VP specs depending on the season ?
- Summer : 45 kPa < VP < 60 kPa
- Interseason : 60 kPa < VP < 90 kPa + VLI < 1150
- Winter : 60 kPa < VP < 90 kPa
Why do we check VLI in interseason ?
To check that we have a high VP and a large fraction distilled at 70°C
What are the two possible routes for ethanol in France ?
- Ethanol incorporated in a fuel
- Ether synthesized from alcohol and olefinic HC from FCC
What is the maximum qty of ether that can be added in a gasoline ?
Maximum 15%
What are the regulated pollutants at the exhaust of a gasolien engine ?
CO, NOx and unburnt HC
What is the current sulfur spec for gasoline ?
Max 10 ppm
Why do we have to redue the sulfur content in the gasoline ?
- To protect the catalyc converter that enables to reduce the emissions of CO, Nox and unburnt HC
- Because of its corrosivity
- It forms sulfur oxides which are pollutants
Why do we want to add oxygenated components in the gasoline ?
- Favorable effect on CO and unburnt HC
- Allows the reduction of the benzene content
What is the problem that we create by adding oxygenated compound in gasoline ?
We now form aldehydes (toxic)
What is the maximum mercaptans content in gasoline ?
RSH content : max 15 mg/kg = 15 ppm
What is the problem with cracked gasolines ?
They are chemically unstable (olefins) and can form gums
What are gums ?
Gums are sticky polymers with a high tendency to plug filters and injectors
They also produce unburnt HC
What are the two tools to monitor gums and gasoline stability ?
We measure both current/existing gums and potential gums
What is the specification for current gums in gasoline ?
Max 5 mg/100 mL
What is the specification of potentialgums in gasoline ?
Oxidation resistance of minimum 6h (at 100°C under O2 pressure)
What kind of additives can we add to help with the chemical stability ?
We can use antioxidants
What are the main gasoline bases ?
- Isopentane (from LVN)
- Isomerate (from LVN)
- Reformate (from IVN)
- Cracked gasoline (FCC, HCK or steam cracker)
- Alkylates
- Butane
- Oxygenated compounds (MTBE/ETBE)
Which is the highest value product from the possible gasoline bases ?
Alkylates is the highest value
