Post Midterm Flashcards
The Kp of a reaction depends on “_____” only?
Temperature
The “______” the Kp, the more complete the reaction
Larger
- As Kp approaches 0 - no reaction
- As Kp approaches ∞ - complete reaction
Affects of pressure on Kp?
Pressure does not affect Kp, however it does affect the equilibrium composition.
If P increases the ratio of partial pressures changes:
- Increases then Δv > 0
- Decreases then Δv < 0
- ΔP = 0 then Δv = 0
Effects of inert gases on Kp?
Kp is not affected by presence of inert gases. However, it affects the equilibirum composition
What happens to Kp when the stoichiometric coefficients are doubled?
Value of Kp is squared
When determining Kp, free electrons in the equilibrium constant can be treated as an ?
Ideal Gas
Exothermic or Endothermic?
- Breaking C-C
- Breaking C-H
- Isomerization
- Polymerization
- Breaking C-C (Endothermic)
- Breaking C-H (Endothermic)
- Isomerization (Exothermic)
- Polymerization (Exothermic)
The 3 Cracking Types
- Thermal Cracking
- Catalytic Cracking
- Hydro Cracking
Properties of Thermal Cracking (Temp, Pressure, O.N)
- 450-650°C
- 80-100atm
- O.N is approximately 85
How does temperature affect thermal cracking?
Effect of temperature is to break the bonds near the ends of the HC
How does pressure affect thermal cracking?
Effect of pressure is to break the bonds near the middle of the HC
How does time affect thermal cracking?
Time increases the amount of breakage
What is Catalytic Cracking and its approximate O.N?
Catalytic Cracking: Process is in the presence of various catalysts and is typically a high quality gasoline with an O.N of approximately 90
What is Hydro Cracking and its properties (pressure, O.N)?
Hydro Cracking: Process is in the presence of a catalyst and a high pressure hydrogen (30-40 atm) with an O.N of approximately 92
What is Reforming and its typical feed?
Otherwise known as Catalytic Reforming, is a process in the presence of a catalyst and hydrogen. The feed is low quality gasoline and some light kerosene.
What is the process called if the catalyst in reforming is Platinum? Approximate O.N?
Platforming and an O.N of approximately 95-98
What are the 12 fuel properties?
- Calorific Value
- Volatility
- Viscosity
- Specific Gravity
- Fire Point
- Flash Point
- Spontaneous Ignition Temp (S.I.T)
- Flame Velocity
- dp (delay period) or Ignition Delay
- Oiliness
- Impurities
- Octane Number
L.H.V of gasoline and diesel fuel?
- LHV)gas = 42 MJ/kg
- LHV)diesel = 42.5 MJ/kg
Affects on the mixture as volatility increases?
Better evaporation and mixing will be obtained
What is Vapour Lock?
When there is only vapour in the pump which results in no flow. This is especially disadvantagous to high volatile fuels.
What is Carborator Icing?
Due to a high rate of evaporation, a layer of ice will cover the device and result in a loss of engine control.
Issues with low volatility?
- Poor Mixing
- Cannot Cold Start
Issues with high volatility?
- Vapour Lock
- Carborator Icing
- Not good for hot starts
2 methods in measuring volatility?
- ASTM Method
- Vapour Pressure (Reid Method)
On an ASTM cruve, what do Ta and Tb indicate?
- Ta = Initial Temp or Bubble Temp
- Tb = End Temp or Dewpoint (First few droplets of condensation when cooling)
On an ASTM curve, what does it mean if Fuel 1’s curve is higher than Fuel 2’s?
- Fuel 1 has more volatile fraction than Fuel 2
- Fuel 1 has more heavy fraction than Fuel 2
Do we need a more volatile or less volatile gasoline in the winter compared to the summer?
More volatile
What happens to the volatility as you move down on a Temperature vs Volume % graph?
Moving down → more volatile
In terms of volatility, what are the 5 steps in running an engine on an ASTM curve?
- Cold Starting/Starting
- Warming Up
- Acceleration/Cruising
- Cruising
- Diluting Lube/Oil and deposits on the surface
What is Cruising?
Running at 80% of max power
Why can’t we use diesel fuel in a petrol engine?
We need a volatile fuel in a gasoline engine. Diesel is less volatile and is not a suitable mixture for combustion.
What does NPSH stand for?
Net Positive Suction Head
What is the Reid Test or otherwise known as RVP (Reid Vapour Pressure)?
- Common measure in the volatility of gasoline, oil, petroleum products except for LPG
- Absolute vapor pressure exerted by a liquid at 100°F (37.8 °C)
- A pressure gauge is used to determine the volatility of the fluid
- The dry air is 5-8 times larger than the fuel
Four methods in measuring viscosity?
- Rotary Viscometer
- Discharge Viscometer
- Bubble Movement
- Falling Ball Viscometer
What is Saybolt Universal Seconds (SUS)?
A measure of kinematic viscosity using time. It is the time that 60 cc of oil takes to flow (discharge method) through a calibrated tube at a controlled temperature, 38°C.
Three types of discharge viscometers and their differences?
- Saybolts (or Furol)
- Redwood
- Engler
Principle remains the same, however it differs by orifice dimensions and discharge volume.
What is the difference between Saybolts and Furol?
SUS is the unit for low viscosity fluids while FUS is for high viscosity
What is a Hydrometer?
Instrument that measures the specific gravity (relative density) of liquids
Higher API gravity indicates?
Lighter fuel
Define Fire Point
Temperature at which the fuel has evaporated enough to burn (by a spark) for at least 5 seconds
Define Flash Point
Lowest temperature at which vapours of a volatile material will ignite, when given an ignition source. The mixture continues to burn.
A low flash point indicates?
Highly flammable (hazardous)
What are the flash points for petrol and diesel fuel?
- Petrol
- T_flash ≃ 60°C (flammable)
- Dependent on composition
- Diesel
- T_flash > 60°C (inflammable)
What is Spontaneous Ignition Temperature (SIT)?
Otherwise known as the autoignition temperature, it is the lowest temperature at which combustion starts without an external source of ignition (spark, flame, etc)
What are the two types of flame velocity?
- Laminar Flame Velocity (S_L)
- Turbulent Flame Velocity (S_T)
5 factors that affect flame velocity?
- Temperature
- Pressure (density)
- Turbulence
- Chemical Formula of the Fuel
- F/A ratio
Impact of temperature and pressure on flame velocity?
Increase in temperature or pressure, increases flame velocity
What is a delay period?
Interval between the spark and the start of combustion
“dp” depends on what 3 factors?
- Temperature
- Pressure
- F/A Ratio
How do temperature and pressure impact dp?
Increase in P or T, lowers dp
At what fuel air ratio is dp lowest?
FA stoic
What is Oiliness?
A measure of tendency to adhere to the surface and causes better lubrication
True or False, is there less oiliness for long chain HCs?
False, for a long chain HC there is more oiliness
Does gasoline or diesel fuel have more oiliness?
Diesel has oiliness while gasoline is considered dry.
Why can’t we use petrol in a diesel engine?
We cannot use petrol in a diesel engine as it will not have enough lubrication and causes seizure
Examples of impurities in fuel
- Sulfur
- Gum
- Ash
What is knock?
Knock is abnormal combustion in IC engines or early combustion of the end charge
What is the mechanism of knock?
High compression as a result of expanding gases due to the flame. This leads to a higher temp causing an explosion before the flame hits.
What are 5 issues as a result of knock?
- Rough running of the engine
- High rate of heat release (hot spots)
- High mechanical and thermal stresses (failure)
- Fouling the surfaces by residues
- Drop in engine efficiency
How is the early spark and late spark figure illustrated in a graph from tdc to bdc?
Refer to Emma’s Notes Combined (page 60/85). The weird sound noises we always do with our hands.
What occurs at optimum sparktiming?
At optimum sparktiming the work loss will be minimum and the torque output will be maximum. Recall what it looks like on the graph.
7 factors affecting knock
FTPFARMEC
- Fuel Type
- Temperature
- Pressure
- Fuel Air ratio
- Mixture Turbulence
- Engine Size
- Compression Ratio
What are the two factors associated with temperature that affect knock?
- Higher flame velocity
- Shorter dp
- When temp increases, the dp is shorter
- Higher T increases knock
How does pressure affect knock?
Increase in P, increases knock
Tendency of knock at what FA ratio?
Due to a shorter dp, the FA stoic has a higher tendency of knock
How does turbulence affect knock?
Higher turbulence, less knock due to higher flame speeds
What is misfiring and how does it occur?
- When the ignition kernel is knocked out
- Excess turbulence may cause misfiring due to blowing out flame kernel (flame nucleus)
How does the engine size affect knock?
Bigger engine, more knock. Longer distance for flame to travel
How does the compression ratio affect knock?
Higher r, higher knock
Level of resistance to knock for iso-octane and n-heptane respectively?
- Iso-octane is very resistant to knock
- n-heptane is very weak to knock
In regards to the otto and diesel cycle, what is MEP?
Mean effective pressure is the average pressure on the piston which gives the same work as the actual cycle. MEP is a measure of the engine torque.
Look at MEP on a PV graph (page 61/85 on Emma’s notes)
What is klmep and klimep?
- klmep: mep at which the engine starts to knock
- klimep: knock limited indicated mep
What is indicated power?
Power from pressure of the piston
What are the compression ratio values for SI and diesel engines respectively?
- SI: r = 10
- Diesel r = 20 or 22
Although the otto cycle efficiency is greater than the diesel cycle, why are diesel engines commonly employed?
- Less emissions
- Higher compression ratio
- Potential for turbo charge
In terms of measurement, what is O.N defined as?
The octane number of a fuel is the volume percent of iso-octance in a mixture of the two reference fuels which has the same resistance to knock as the fuel.
Two references:
- n-heptane (0 O.N)
- iso-octane (100 O.N)
Two standard engines used to measure O.N?
- CFR (cooperation fuel research)
- BICERA engine
Procedure in measuring O.N using a CFR engine?
- Adjust P, T, rpm, spark advance, etc
- Increase r by moving cylinder head
- See which r engine begins to knock
- Check which combinations of reference fuels give us knock at this r
Two compounds to enhance O.N? Additive to decrease O.N?
- Increase O.N (although poisonous)
- TEL (tetraethyl lead)
- TML (tetramethyl lead)
- Decrease O.N
- Nitrates
Two methods in measuring O.N and there properties (rpm, T_inlet, Spark Timing) ? Which is typically lower?
- Research (RON)
- 600 rpm
- T_inlet = 25°C
- Spark Timing = 13° btdc
- Motor (MON)
- 900 rpm
- T_inlet = 149°C
- Spark Timing = 19-26° btdc
- MON is lower than RON 8-12 times
5 chemical structure changes that can increase the resistance to knock
- Compacting the structure
- Adding methyls to the second carbon
- Two or more double bonds in olefins
- Aromatics
- Branching chains
2 chemical structure changes that can decrease the resistance to knock
- Parrafins: increase chain length
- Introducing long chains to the main ring
Affect of one double bond to O.N?
No effect but two or more double bonds increase O.N
Which has a higher resistance to knock Aromatics or Napthtenes?
Aromatics
Three key factors in knock resistance
- Long dp
- Fast flame speed
- Short distance for flame to travel
How does a high O.N impact the combustion ratio and engine efficiency?
- Higher O.N allows for higher combustion ratio
- O.N does not increase efficiency
- only indirectly if r increases
What is the knock in diesel engines related to?
Sudden explosion of the particles that already existed in the cylinder
What is the difference between the affects of dp in a gasoline engine and a diesel engine?
A longer dp is preferred in a gasoline engine, while a good diesel engine requires a short dp to avoid accumulation of too many particles to ignite
2 types of diesel engines?
- Direct Injection
- In-direct Injection
3 factors affecting dp in diesel engines
- Temperature
- Pressure
- Better mixing of fuel and air reduces dp
How does temperature and pressure affect diesel knock?
Increasing T or P reduces diesel knock
3 methods to create swirl in high speed diesel engines
- Direct port
- Helical
- Masked Valve
Diesel knock when dP/dθ is very high
See graph in Emma’s notes (pg 69/85)
5 key parameters for Diesel Fuel
- Cetane Number CN
- Diesel Index D.I.
- Cloud Point
- Pour Point
- Effects of factors on dp
What is the level of resistance to diesel knock for Cetane C16H34 and alpha-methyl-napthtalene C11H10?
- Cetane has good resistance to diesel knock and a relatively short dp
- Alpha-methyl-napthtalene is the weakest fuel against diesel knock
What does the CN of a fuel represent?
Percentage of n-cetane in the mixture of n-cetane and alpha-methyl-napthtalene which has the same combustion characteristics of the fuel under testing
As alpha-methyl-napthtalene is very expensive, what is an alternative reference fuel?
Hepta-methyl-nonane
What does a higher CN represent and what is the range indicating a good fuel?
- Higher CN represents a short dp
- CN 55-70 is a good fuel
Define Aniline Point and its typically value
- Aniline Point is the lowest temperature at which the diesel fuel and aniline are completely soluble
- Typically 120°F (49°C)
What is an Aniline?
Amino Benzene
A higher DI corresponds to a “_____” CN?
Higher DI, higher CN
Define Cloud Point. When is it suitable for cold weather operation?
- Highest temperature at which a haze or a cloud of wax crystals appear in the fuel
- If the cloud point is low, it is suitable for cold weather operation
Define Pour Point. What is the ideal pour point?
- Highest temp at which the fuel doesn’t flow for 5 seconds when the container is kept horizontal
- A low pour point is ideal
How is the power increased in a supercharged engine? Why is this not possible for a petrol engine?
- The inlet pressure is increased by the compressor and the power increases
- Cannot do for petrol as a shorter dp results in increased knock
What is it called when the power of a supercharger is provided by a turbine on exhaust gas?
Turbocharger
What are 3 motions in the cylinder of an engine for better utilization of fuel (better combustion)?
- Diesel Engine
- Swirl
- Squish
- SI Engine
- Turbulence
- Shouldn’t be too much motion or it can contaminate the next fuel stream
Where’s the hottest part in the engine?
Exhaust valve
Which is lower Tpour or Tcloud?
Tpour
Name 4 additives for fuels
- Oxidation Inhibitors
- Prevents gum formation and fouling of spark plug and exhaust valve
- Corrosion
- Detergents
- Anticing Additives
- 5 dyes to distinguish various fuels
Define pre-ignition. How can you tell if this occurs?
- Very advanced combustion by hot spots
- hot points (spots) are residuals on the exhaust valve or spark plug which are hot enough to ignite before the spark does
- You can tell if you disconnect the spark plug but the engine is still running
What causes pre-ignition?
- Knock causes pre-ignition
- Pre-ignition also results in knock
How to resolve pre-ignition issues?
- Run engine at full throttle, this detaches the hot spots from the exhaust valve
- Full throttle leads to very high turbulence
Name 5 other fuel types
- Ethanol and methanol
- High ON, renewable
- Gasohol
- Biodiesel fuels
- Vegetable oil
- Soybean oil
- DME (dimethyl ether) for diesel
- high CN approximately 55
- Mixture of biodiesel and petrodiesel (ex. B20 indicates 20% bio)
What is Fischer-Tropsh Diesel? Which is more expensive between this and petrodiesel?
- Synthetic fuel (liquid) which comes from syngas (H2 & CO) and some other HCs
- Petrodiesel is cheaper
Process in measuring CN
- CFR engine
- Ignition Angle: 13° btdc
- Change r and adjust combustion at tdc
- Check what mixtures of reference fuels have dp of 13°
What is the power output if 1KW is used to compress the inlet air in a diesel engine?
50 kW
Gaseous fuels are typically found in nature or manufactured, name examples of each.
- Nature
- Natural gas
- Coal mine methane
- Manufactured
- Solid
- Liquid
- Fermentation of organic wastes
Composition of natural gas?
Mainly methane (80-95%), ethane, CO2, N2, water, S, some light HCs (hydrates)
What is the boiling temperature for methane and what does it result in?
- Tboil = -162°C
- Results in LNG
5 gaseous fuels from solid fuels
- Producer gas
- manufactured from material such as coal
- Water gas (blue gas)
- composed of CO and H2 (ex. passing steam over hot coal)
- Carburetted water gas
- When heavy HCs are added, results in CO, H2, and light HCs
- Coke oven or blast furnace gas
- Landfill gas
What are the heating values for rich and lean gaseous fuels?
- Rich: HV > 16 MJ/Nm3
- Lean: HV < 8 MJ/Nm3
- T = 25C, P = 1 atm
Two critical properties for gaseous fuels?
- Heating value
- Specific gravity
Number of families based on the Wobbe Number?
- Family I (Low Wobbe Number)
- Family II
- Family III (High Wobbe Number)
What are the reference fuels for MN?
- Methane (100 MN)
- Hydrogen (0 MN)
What is a mercaptan?
Otherwise known as Methanethiol, mercaptan is an oderant additive for inspection of natural gas. They are mainly thiols (R-S-H)
What are hydrocarbons seperated from natural gas called?
NGL (natural gas liquid)
What is LPG and what does it typically consist of?
- Liquified petroleum gas
- Mainly propane and butane mixed at 50/50 (some propylene and butylene)
- Winter can result in 70% propane, 30% butane
Boiling points of propane and butane?
- Propane Tboil = -42°C
- Butane Tboil = 0°C
Why is propane more hazardous than methane?
Propane is heavier than air
What are two conditions for NOx?
- High T
- Excess oxygen
- In diesel engines, NOx is more important and higher where CO is minimal (CO requires lack of O2)
Name the 4 emissions from combustion
- CO
- Unburned HC (UHC)
- Oxides of Nitrogen (NOx)
- Particulates
CO and UHC are caused by what two factors?
- Oxygen deficiency
- Quenching of flame
How does soot form?
- Deficiency in O2
- Diesel engines, accelerate the car due to high concentration of fuel and high temp which results in some kind of pyrolysis
What must be present for UHC and humudity to create smog?
Sunlight
What is EGR?
- Exhaust gas recirculation
- Technique to reduce NOx by recirculating the exhaust gas back to the engine cylinders
- This dilutes the O2 in the incoming air stream and provides gases inert to combustion to act as absorbents of combustion heat to reduce peak in-cylinder temperatures
- Lower T, lower NOx
Does petrol or diesel have higher gas exhaust temperatures? Why?
- Petrol
- The compression ratio is larger in diesel engines so more heat is converted to work resulting in lower exhaust T
Device to measure CO emissions?
- Non-dispersive Infrared Analysis (NDIR)
- CO can absorb infrared radiation with specified wave length
- By flowing CO into the upper pipe, less energy is recieved by the container and the deflection of the diaphragm is a measure of CO
Device to manage UHC and NOx emissions respectively?
- Flame Ionization Detector (FID)
- Chemiluminescent device
- higher concentration of NO2 emits intense light
5 factors determining reaction rate
- Physical state of the reactants
- Temperature at which reaction occurs
- Concentration of the products
- Presence of a suitable catalyst
- Pressure of reactants
What is petroleum and what is it made from?
- Complex mixture of a wide range of compounds of varying complexity mostly of the HC type
- Mainly marine and animal life deposits over millions of years under the combined action of time, P, and T
Resources of complex and heavy HCs are potentially available in the form of what?
Oil sands and shale oil deposits
Where is petroleum typically found trapped in?
Trapped in certain rock formation usually over pockets of salt water and often associated with natural gas
As oil comes out of the ground what other compounds are also present?
- Sulfur
- Oxygen
- Nitrogen
- Variety of salts and minerals
What is considered a more desirable and economically valuable oil?
Oils with high proportions of light distillates and low concentrations of sulfur compounds are considered more desirable than sulphurous and high viscosity heavy oils
What is a seismic survey?
- A geophysical exploration method developed to ascertain underground rock formations and conditions
- Produces shocks waves in the ground
- Reflecting waves are studied
What is HDD?
Horizontal directional drilling is a steerable trenchless method using a surface-launched drilling rig, with minimal impact on the surrounding area
What is an oil reservoir?
Porous sedimentary rock formation capped with a layer of impermeable rock through which liquids and rock cannot pass
Approximately what percent of reservoirs can be extracted?
20% can be extracted with 80% remaining in the pores of the rocks
What is porosity?
Volume of all the pores in a reservoir rock normally expressed as a percentage of the total rock volume, typically ranging from 10-30%
What is permeability?
Quantifies the capacity of a porous material to transit fluids under the application of a pressure difference
What is EOR? Name three production methods
- Enhanced Oil Recovery is the implementation of various techniques for increasing the amount of crude oil that can be extracted from an oil field
- 3 Production Methods
- Primary Production
- Secondary Production
- Tertiary Production
What are two secondary production methods associated with EOR?
- Water flooding
- Natural gas injection
When is tertiary production applied? Name the 3 methods
- Applied when secondary has been exhausted
- 3 methods
- Miscible
- Chemical
- Thermal
What is the miscible method in EOR?
Hydrogen and CO2 solvent flooding is applied
What is the chemical method in EOR? Examples?
- Water with suitable chemical additives are injected into the formation. These include:
- Polymer flooding
- Akaline flooding
- Surfactant polymer injection
- Utilizing caustic
What is the thermal method in EOR? Examples?
- Steam injection is applied to heat the reservoir so as to decrease the viscosity of the oil. Methods include:
- Steam simulation
- Steam flooding
- In-Situ combustion
- SAGD
What does the typical structure of oil sands consist of?
Sand grains surrounded by water, bitumen (10%), with some clay (contains some metals such as Ni and Vanadium) and mineral particles in between
What is Shale Oil?
A tar like substance contained in the rocks, shale oil comes from oil shales (extracted by fracking)
7 examples of refinery processes
- Hydrogenation
- Dehydrogentation
- Cracking
- Formation
- Catalytic Cracking
- Polymerization
