Analysis of Fuel and Lube Oil Flashcards
what is meant by flue gases?
a mixture of gases produced by the burning of fuel
what are exhaust gas analysers used for?
used to diagnose engine emission problems and thereby maximize engine performance. Gas analysers deliver reliable and accurate measurements quickly and help with emission compliance. They are used to determine the amount of carbon monoxide and other gases. Both Infrared gas analysers and chemical gas are used to find real-time combustion efficiency using the measurements of gases. Other uses include checking evaporative emission system operation, no-start conditions, exhaust system leaks, evaporative emission system leaks
why is composition of exhaust gas important in marine engines?
Marine engines rely on the composition of the exhaust gas to give feedback to the combustion controller, which will modify the settings that control the start of the process to keep the engine as efficient as possible. Emission from the ships funnel have to be correct for the area that the vessel is sailing within. If the composition of the flue gases isn’t correct the ship will be due for a heavy fine. An Exhaust Gas Analysers are used to measure exhaust gases caused by combustion. Also known as an emission gas analyser, it effectively measures different gases present and gives readings about their content. Some gas analysers can also identify the sources that can cause a fire if fuel is released inadvertently. some models can even determine engine efficiency.
what is the problem with burning HFO?
The problem with burning heavy oil is its not a high quality fuel because it contains chemicals such as sulphur that when added to combustion process and combined with other chemicals has detrimental effect on the atmosphere when emitted from the exhaust funnel. today ships use variations of HFO like for example VLSFO to reduce emissions.
what working principles are used to monitor flue gas?
Monitoring of flue gases depends upon on the equipment using one or more of the following principles
1.Spectroscopic absorption
2.Luminescence
3.Electro analysis
4.Paramagnetism
5.Laser technology
explain what is meant by Dissociation?
Majority of combustion reactions are reversible. At high temperatures molecule bonds that have formed during combustion tend to disrupt and reform molecules of the original elements and compounds, absorbing heat in the process. Gas mixtures and rich oxygen contents tend to reduce dissociation considerably. Once temperature falls molecules reform and heat is again evolved. Thermal decomposition is non reversible split up under heat, whereas thermal dissociation is reversible split up under heat. In an IC engine dissociation causes reduction of maximum combustion temperatures and heat re-appearance during expansion occurs, which raises the curve above the adiabatic.
explain what is meant by an adiabatic process?
A process or condition in which heat does not enter or leave the system concerned. Adiabatic process means a process that neither allows the heat to transfer inside nor lets the heat out of the system.
what are exothermic and endothermic reactions?
Exothermic reactions are those involving heat evolution, as are most combustion reactions, but some are endothermic and require heat supplied externally. When energy is transferred to the surroundings, this is called an exothermic reaction and usually feels hot. When energy is taken in from the surroundings, this is called an endothermic reaction and usually feels cold
what are the combustible elements in fuel?
Combustible elements in fuel are carbon (C), hydrogen (H2) and sulphur (S). These combustibles when supplied with oxygen (O2) from atmospheric air combust and liberate heat.
what is sulphur dioxide and how is it formed?
Sulphur dioxide is a colourless gas with an irritating pungent odour. It readily dissolves in water and is one of the main chemicals that causes acid rain. Sulphur dioxide is a common air pollutant. Almost all sulphur dioxide found in atmosphere is due to human activity. However reaction in IC engines also makes a significant contribution to this total. Sulphur dioxide is detrimental to human health and is formed when sulphur in fuel combines with oxygen during the heat of the combustion process.
Why is there sulphur in fuel?
The sulphur is in most crude oils that are taken from the earth, and usually no sulphur is removed during refining process. However the sulphur is now being removed to have low sulphur fuel oil to produce low sulphur emissions from diesel exhaust gas and comply with MARPOL annex VI. The acid formed due to burning of sulphur also cause problems in air heaters and economizers. In lC engines this effects the cylinder liners and exhaust valves, especially where exhaust valve has a water cooled cage. The dew point can also be reached when exhaust flows through the economizers and exhaust gas boilers causing corrosion of the heating surfaces of these items. Its therefore important to have scavenge temperature at the correct value because if engine runs with low scavenge temperature the exhaust temperature is lower. This means dew point is reached and acids form at an early stage and components are subjected to these acids and they cant withstand them so get severely damaged.
what is meant by calorific value?
The calorific value is the total energy released as heat when a substance undergoes complete combustion with oxygen under standard conditions.
why are NOx emissions important?
The NOx emissions are of concern because they’re associated with increased acidity of particles, cloud water and precipitation (acid rain), causing damage to plant and marine life and its an irritant to human respiratory system. NOx is important part of the formation of photochemical smog and atmospheric oxidants. However reducing NOx, from IC engines is another problem. Replacing some of the excess air with recirculated exhaust gas reduces the overall content of nitrogen and excess oxygen in the combustion cycle and also has the effect of reducing heat loss to the fresh nitrogen drawn in with the air. Another important thing is to reduce the peak temperatures that are producing NOx. The use of EGR (exhaust gas recirculation) and miller cycle linked with two stage turbo charging are the two main strategies as well as exhaust gas scrubbing technology.
why is nitrogen important?
Nitrogen is important due to the way it moves through the combustion process and changes into nitrogen dioxide and nitrous oxide. The high peak temperatures of combustion causes the nitrogen to oxidise and then released into engine exhaust system and then to atmosphere if not stopped in some way.
why are low sulphur fuel used?
Sulphur in exhaust gas is also a problem because it combines with oxygen and hydrogen and forms sulphur dioxide and sulphur trioxide and can combine with water droplets to form acid, which is the reason for using low sulphur fuels.
what is meant by adiabatic flame temperature?
The adiabatic flame temperature (AFT) is the temperature attained when all of the chemical reaction heat releases heat combustion products. When a combustion reaction takes place energy is released to the combustion products. If no heat is lost in this process, the temperature of the combustion products is known as the “Adiabatic Flame Temperature.” Varies with fuel type. Typical figures for gaseous fuels would be methane 1,8272℃, hydrogen 2,037℃, carbon monoxide 1,957℃. These values being theoretically calculated, actual values are more difficult to measure
what is meant by oil fuel additives?
Fuel additives are chemical compounds formulated to enhance the quality and efficiency of the fuels used. Environmental legislation to reduce emissions and improve fuel economy has a significant impact on fuel formulations and engine system design. Fuel Additives help save money in the long run. Despite the many different types of fuel additives, the main reason for using fuel additives is to save money on fuel bills. an example of a oil fuel additive is Exocet Marine Fuel Conditioner, which is a multi-functional marine fuel additive suitable for use with Gas Oil and Marine Gas Oils (MGO) including all grades of distillate marine fuels; DMA, DMB, DMX, DMZ used in high speed diesel engines.
Briefly explain the following marine fuel grades
DMX
DMA
DMZ
DMB
DMC
RM
DMX is a special light distillate intended mainly for use in emergency engines. Light distillateshave the lowest boiling points, consist of short hydrocarbon chains, and are flammable substances which can be in either a gaseous or liquid state
DMA (also called marine gas oil, MGO) is a general purpose marine distillate that must be free from traces of residual fuel. DMX and DMA fuels are primarily used in marine engines
DMZ has a higher minimum viscosity than DMAbut is otherwise identical in its characteristics to DMA marine gas oil.
DMB (marine diesel oil, MDO) is allowed to have traces of residual fuel, which can be high in sulphur. This contamination with residual fuel usually occurs in the distribution process, when using the same supply means (e.g., pipelines, supply vessels) that are used for residual fuel. DMB is produced when fuels such as DMA are brought on board the vessel in this manner.
DMC is a grade that may contain residual fuel, and is often a residual fuel blend.
Residual (non-distillate) fuels are RM These fuels are also identified by their nominal viscosity (e.g., RMA10, RMG35, etc.) Nominalviscosity represents an average value within the respective viscosity class
what do chemical tankers have to comply with?
The vessels have to comply with MCA recommendations before an IMO certificate of fitness for the carriage of dangerous chemicals in bulk is issued under SOLAS chapter VII. The IMO conventions require chemical tankers built after 1st of July 1986 to comply with the international bulk chemical code (IBC Code). This provides international standards for the safe transport by sea of dangerous liquid chemicals in bulk.
what is the risk of low flash point products?
With low flash point products the danger may exist that the atmosphere lies between the LEL and the HEL therefore creating the risk of explosion. Typical flash points are pentane -49℃,hexane -23℃,heptane -4℃ (aliphatic hydrocarbons), benzene -11℃,(aromatic hydrocarbon), acetone -18℃ (ketone), methanol 10℃ (alcohol), carbon disulphide -30℃. vapour pressure is constant pressure during isothermal isobaric evaporation (or condensation), when liquid and vapour are in equilibrium (quality defined by dryness fraction). LEL and HEL are affected by variations in vapour pressure.
what is HEL and LEL?
Before a fire or explosion can occur, three conditions must be met simultaneously.
A fuel (i.e.. combustible gas) and oxygen (air) must exist in certain proportions, along with an ignition source, such as a spark or flame. The ratio of fuel and oxygen that is required varies with each combustible gas or vapour.
The minimum concentration of a particular combustible gas or vapour necessary to support its combustion in air is defined as the Lower Explosive Limit (LEL) for that gas. Below this level, the mixture is too “lean” to burn. The maximum concentration of a gas or vapour that will burn in the air is defined as the Upper Explosive Limit (UEL) or (HEL) higher explosive limit . Above this level, the mixture is too “rich” to burn. The range between the LEL and UEL is known as the flammable range for that gas or vapour.
what is meant by TLV?
The threshold limit value (TLV) gives concentration of a substance in air in ppm which can be breathed in without harmful effects but there is a time limit that must not be exceeded. Maximum limit being five consecutive daily 8hour exposure. Typical TLV values are anilene (5), carbon tetrachloride (10), benzene (25), methanol (200) but the value can be very low, under 0.02, for certain chemicals. A number of chemicals have toxic limits well below their combustible air/gas concentration ratio and its unsafe to enter spaces even if gas concentration falls below lower explosive limit (LEL).
what are the three type of crude petroleum
Crude petroleum can be classified into three types
1.Paraffin base in which the residue after distillation contains more than 5% paraffin wax
2.Asphalt base in which the residue after distillation contains less than 2% paraffin wax and is mainly composed of asphalt (bitumen)
- Mixed base in which the residue after distillation contains between 2% and 5% paraffin wax mixed intimately with asphalt
The type obtained depends on the source and determines the type of refining carried out and type of products produced at the end. Raw petroleum at the well head is often associated with natural gas, which has high methane content, this gas can be directly utilised and is piped off for domestic use. Primary separation, by heating and cooling, will allow a yield of well head motor spirit (straight run gasoline). The bulk of the crude is taken to the refinery for processing into a wide range of products depending on the type of crude. Asphalt is mainly found in residue oils and is an indefinite substance, both hard and soft, being mainly combustible although hard asphalt can cause considerable gum deposits in the IC engines.
what is the composition of petroleum?
Petroleum in all its form consists of hydrocarbons, with small amounts (up to 5%) of nitrogen, oxygen sulphur, metallic salts, etc., together with water emulsified in the oil and associated with natural gas.
what are hydrocarbons and what are the 4 main series?
hydrocarbon is an organic chemical compound that is composed exclusively of hydrogen and carbon atoms. Hydrocarbons are naturally-occurring and form the basis of crude oil, natural gas, coal, and other important energy sources. The exact proportions and compositions decide the character of the petroleum as well as the refining processing equipment used. Hydrocarbons are made up of at least nine recognisable series, a series being a range of products with the same molecular structure pattern.
The four main series are
Paraffins
Naphthenes
Aromatics
Olefines
The first two are classed as saturated and the other two are unsaturated. Unsaturated series are rarely found in crude petroleum but can be found by molecular bonding alternation during later processing. olefines and naphthenes have the same C:H ratio and are distinguished by their difference in molecular structure. The lowest members of any series are gases, graduating to liquids as the molecular structure becomes more complex, thence to semi solids and to solids . For example , the paraffin hydrocarbon series methane to butane are gases, pentane to nonane, which are liquids of decreasing volatility. By octadecane there is a mineral jelly and further up the series lies paraffin wax solid. With slight deviations from the molecular grouping system, millions of different combinations called isomers are possible.
explain what is density and how is it measured?
Density is the measurement of how tightly a material is packed together. It is defined as the mass per unit volume. Density Symbol: D or ρ Density Formula: ρ = m/V, where ρ is the density, m is the mass of the object and V is the volume of the object. density is related to temperature and If temperature cant be fixed at 15℃,like for instance with high viscosity oils, then a correction factor per ℃ above the 15℃ is added to the observed density, or if measured below 15℃ is subtracted from the observed density. Density is measured by a hydrometer. The datum temperature is 15℃ and the reciprocal of density is specific volume (m3 /kg). Density is important because when fuel is ordered by the weight and delivered by volume there’s always a chance of the density being incorrect. Density is also proportional to the energy extracted, therefore there will be a reduction in performance if density is lowered. Marine fuel density meter are available on-board. On-board test equipment also measure the CCAI (calculated carbon aromaticity index) for residual fuel oil . Mass flow meters are also installed which measure incoming bunker fuel coming on-board.
a.) what is viscosity?
b.) what is absolute dynamic viscosity?
c.) what is kinematic viscosity?
a.) Defined as the resistance flow rate of a fluid. Fluid changes flow rate and shape due to internal molecular friction of molecule against molecule of the fluid, which produces a frictional drag effect. Increase in temperature has the effect of reducing viscosity. To achieve correct atomization of fuel you have to heat up the fuel that has high viscosity to reduce viscosity to about 20cSt at the fuel injector and about 13cSt for internal combustion common rail engine system. The viscosity of diesel oil is about 7cSt at 38℃.When providing a value for viscosity you have to also quote temperature otherwise value is meaningless for comparison. Scale readings between viscometers can be related to each other by graphs or the use of constants. Its not possible to calculate viscosities at different temperature without using a viscosity temperature curve. Each oil and blend type is different with the effect of temperature change so a curve is required for each type. Sulphur content is falling dramatically due to pressure being put on the industry to reduce atmospheric pollution.
b.) Absolute (dynamic) viscosity is used for calculations is difficult to determine due to it being numerically equal to that force to shear a plane fluid surface of area 1m2, over another plane surface at the rate of 1m/s. when the distance between the the two surfaces is 1m.
c.) Kinematic viscosity is the ratio of absolute velocity to the density at the temperature of the viscosity measurement. Kinematic method is chosen to determine values in the ISO fuel specification. viscosity is expressed in centistokes (cSt) or mm2/s. Kinematic viscosity is expressed in centipoise (cP) and measured by a capillary flow of a set liquid volume from a fixed head. For practical purposes viscosity is measured on on a time basis. Its measured as the number of seconds for the outflow of a fixed quantity of fluid through a specifically calibrated instrument at a specified temperature. Temperature accuracy is vital , a variation of + or - 0.1℃ is a maximum for temperatures up to 60℃.
who are the ISO?
The International Standards Organization (ISO) sets classifications for marine fuels that are supplied on a world-wide basis (Marine fuels are specifically covered under ISO 8216 and 8217).
what is a viscometer?
Viscometer is an instrument used for measuring the viscosity of a fluid. In the capillary tube viscometer, the pressure needed to force the fluid to flow at a specified rate through a narrow tube is measured. Capillary U tube viscometer can be used. The oil is raised to start position by a suction applied at the top of the right hand section of the tube. As this position is reached the suction is released and the oil is left to fall through the capillary under its own weight. Time is measured from the start point until oil level reaches the end point
explain three factors that are influenced by viscosity
Factors that are influenced by viscosity
frictional drag effect,
pipe flow losses,
fouling factor
frictional drag is caused by the friction of a fluid against the surface of an object that is moving through it. also Fluid changes flow rate and shape due to internal molecular friction of molecule against molecule of the fluid, which produces a frictional drag effect
pipe flow loses refer to when a liquid or gas flows along a pipe, friction between the pipe wall and the liquid or gas causes a pressure or head loss. This pressure or head loss is an irreversible loss of the fluids potential energy. Calculating this loss is fundamental to the design of any pipeline system.
fouling factor represents the theoretical resistance to heat flow due to a build-up of a layer of dirt or other fouling substance on the tube surfaces of the heat exchanger
what is viscosity index?
Viscosity index
A numerical value that measures the ability of an oil to resist viscosity change when temperature changes. High viscosity index refers to oil that is capable of maintaining a fairly constant viscosity value despite wide variations in temperature. Value of viscosity index is determined from a chart based on knowledge of viscosity values at different temperature. On-board a ship viscosity index is important for deck equipment, emergency generators and lifeboat engines. These may be required to be operated at large range temperatures during winter months.
why is it important to restrict sulphur in fuel?
Restricting the sulphur in marine fuel oil and meeting its obligations is important for restricting air pollution. Problem is that the very low sulphur option for use in emission control areas (ECA) is only available in diesel oil, which is more expensive than residual fuel oil and in short supply. Another problem is specification for marine diesel is basically the same as for automotive diesel but flashpoint is different , 60 for marine and 55 for automotive, there would also need to be a change in SOLAS for the maritime industry to have access to wider availability of automotive diesel. The limits on sulphur is to reduce SOx and particulate matter from the emissions of power plants on ships. Annex VI regulation 4 allows flag administration to use alternative methods of compliance with exhaust emission limits
what are some ISO specifications for marine fuels
Bunkers should be ordered to the most up to date specification and checks made that fuel delivery is in accordance with specifications.
DMX and DMA are considered as representatives of marine gas oil (MGO), while DMB and DMC are representatives of marine diesel oil (MDO).
Residual fuel products are as follows: RMA and RMB are fuels for use at low ambient temperature, they have a low pour point and wouldn’t necessarily require heat in storage tanks; RMD, RME and RMG are fuel requiring a standard treatment plant; RMK is very heavy residual fuel oil that requires a special treatment plant to handle such fuels.
DMX is the low sulphur product fuel used in ECAs.
A general rule is the heavier the oil the higher the viscosity and flashpoint and the lower the calorific value.
The following tests are of extreme importance to IC engines
Explain what is meant by octane, cetane number and crankcase dilution.
Octane number
This is indicative of the knock rating. Knocking or pinking are characteristics of some IC engine fuels , particularly in spark ignition engines. It can cause pre-ignition, overheat and damage. Normally on spark initiation the flame front proceeds through the mixture at a speed of about 18m/s. if, due to engine conditions or type of fuel used, the mixture in the front of the flame front has its temperature and pressure raised above the spontaneous ignition point the auto ignition occurs. By the time the last gas charge is reached the flame front speeds can reach 2.2km/s and detonation, temperature rise and heavy shock waves occur. Knocking tendency is dependant on many variables such as revs/s, compression ratio, turbulence, mixture strength and if a hot spot has developed due to a build up of carbon.
Cetane number
Indication of the ignition quality of diesel oil with CCAI being the measure applied to residual fuels. In a compression ignition engine, cold starting is often required, here the time interval between fuel injection and firing, called ignition delay, must not be too long otherwise collected fuel will generate high pressure when it ignites and diesel knock results. Paraffin hydrocarbons have the best ignition quality and are therefore more suitable. Speed and Cetane number can be correlated for high speed engines (above 13revs/s) cetane number of 48 can be regarded as a minimum, ISO sets 35 as minimum for diesel oil. Diesel fuel used in hot petrol engine would cause detonation, that is it has a low octane number. Cetane is a paraffin hydrocarbon, hexadecane being its correct designation, of high ignition quality and is taken as the upper limit of 100. Alpha-methyl-napthalene is of low ignition quality and is taken as the lower limit of zero. Cetane number is numerically the percentage by volume of cetane in a mixture of cetane and alpha-methyl-napthalene that matches the chosen fuel in ignition quality
Crankcase oil dilution
This is the percentage of fuel contamination of lube oil occurring in IC engines, which can reduce the lubricity of oil. The lubricating oil sample is mixed with water and heated, and fuel volatiles are carried over when steam vapour is formed. By condensation of these vapours and separation, the fuel content can be measured and can be expressed as a percentage of the original lube oil sample by mass. Its important to check the lube oil for water contamination and for this another separation test with heating is carried out. Severe corrosion of crankshafts has been caused by sulphur products from fuel oil mixing with any water in lube oil which forms sulphuric acid, which is then carried around the lube oil system.
