Mechanical Engineering Dictionary-C.I Engines

Important Terms and their Meaning of Mechanical Engineering- Combustion Ignition Engines:

ACCUMULATOR – A device used for storing liquid under pressure (sometime used to smooth fluid flow).

ADVANCE (injection timing) – To set the timing of the injection pump or injectors for an earlier injection.

AFTER BURNING – The burning of fuel that is left in the combustion space when the fuel injection stops.

AFTER COOLER – A device used on turbocharged engines to cool the air which has undergone compression, before its entry into the engine cylinder.

AIR CELL – A small auxiliary combustion chamber used in certain types of compression ignition engines, for promoting turbulence and improving combustion.

AIR FUEL RATIO – At full load operation, the air fuel ratio is at least 35 to 50 percent greater than the stoichiometric value. Air fuel ratio in a normal diesel engine varies from around 100: 1 at idle speed to about 30: 1 at full load.

AIR INJECTION SYSTEM – The system which injects the required quantity of fuel into the combustion space with the aid of compressed air.

AIRLESS INJECTION – Injection of liquid fuel into the cylinder of an oil engine by a high pressure fuel pump, so dispensing with the compressed air necessary in the early diesel engines. Also called SOLID INJECTION or MECHANICAL INJECTION.

AIR STARTING VALVE – A valve which admits compressed air to the air starter for starting purposes.

AIR VENT – Arrangement that helps to remove air from the fuel injection system.

ANTECHAMBER – A small auxiliary combustion chamber, used in some compression ignition engines, in which partial combustion of fuel takes place and this is used to force the burning mixture into the cylinder, so promoting more perfect combustion.

ATOMIZATION – The breaking up of fuel jet into fine particles as it is sprayed into the combustion chamber.

ATOMIZER – A device which disperses liquid fuel into fine particles (pulverized spray).

BIFUEL ENGINE – has two injectors to inject two fuels. In this a small amount of a suitable auxiliary fuel is injected into the cylinder either during the intake stroke or early in the compression stroke. Slightly latter in the stroke, the primary fuel is injected.

BLUE SMOKE – The smoke that results from the burning of lubricating oil that reaches the combustion chamber.

BOSCH METERING SYSTEM – A fuel metering system in a diesel engine, with a helical groove in the plunger which covers and uncovers ports in the pump barrel and thereby varies the effective stroke of the fuel pump.

CAVITATION – The formation of cavities in the fluid due to excessive speed of the activator resulting in loss of efficiency in the pump.

CHEMICAL DELAY PERIOD – The time that elapses between the beginning of chemical reaction and the begining of ignition.

CLOSED TYPE NOZZLE – A hydraulically operated, spring loaded needle valve, which opens inward under the pressure acting on the differential area of the needle valve (which is a cylinder lapped in with the body and seated by a spring when the fuel pressure is reduced sufficiently).

COLD SMOKE – The smoke that is made up of droplets of unburned or partly burned fuel or due to water vapour. Also called WHITE SMOKE.

COMBUSTION CHAMBER – The space wherein combustion of fuel with air takes place, more or less equal to the clearance volume.

COMBUSTION SWIRL – Air motion created by the ejection of the combustion products from the pre-combustion chamber into the clearance space above the piston.

COMMON RAIL SYSTEM – The fuel injection system which consists of a high pressure pump which distributes the fuel to a common rail or header to which injectors are connected.

COMPRESSIBILITY – The property of a substance by virtue of which its density increases with increase in pressure.

COMPRESSION IGNITION – Ignition of fuel due to the heat of compression.

COMPRESSION SWIRL – Rotary motion given to air, as the air is forced, during compression stroke, from the cylinder into the spherical or cylindrical combustion chamber through the throat which is located tangential to the combustion chamber.

CONSTANT PRESSURE COMBUSTION – Combustion which occurs without a change in pressure. In an engine, this is obtained by a slower rate of burning than with constant volume combustion.

CONTROLLED COMBUSTION – During uncontrolled combustion, high temperature and pressure prevail within the combustion chamber. After this combustion, fuel that is injected burns without any delay. By controlling the rate of injection, complete control is possible over the rate of burning.

CONTROL RACK – A toothed rack that runs along the upper end of the fuel pump and engages pinions (gear teeth) on each pump plunger to control the amount of fuel injected and thereby determines engine power output.

CRITICAL COMPRESSION RATIO – Lowest compression ratio at which any particular fuel will ignite by compression under prescribed test procedure. The lower the critical compression ratio the better ignition qualities the fuel has.

DEGREE OF ATOMIZATION – is indicated by the smallness of the size of the particles in the spray and also by the smallness of the variation in the size of the particles.

DELAY PERIOD – Time interval between the start of injection and beginning of combustion as indicated by a rise in the pressure crank angle curve, from the curve which represents compression and expansion of air while motoring. Also called IGNITION DELAY.

DELIVERY VALVE – A spring loaded valve mounted at the top of the fuel injection pump barrel. This helps to cut off fuel spray from the nozzle tip abruptly and without dribble.

DEPTH FILTER – Fuel filter which has dozens of layers of porous material arranged in sequence and this arrangement compels the contaminant particles to follow tortuous path into the media.

DIESEL CYCLE – An engine cycle of events in which air alone is compressed and fuel oil is injected at the end of the compression stroke. The heat produced by compressing the air ignites the fuel oil, eliminating the need for spark plugs or a spark ignition system.

DIESEL ENGINE – An engine that operates on the diesel cycle and burns diesel oil by the heat of compression of air.

DIESEL INDEX – A rating of fuel according to its ignition qualities. The higher the diesel index number, the better is the ignition quality of fuel.

DIESEL KNOCK – Sudden, steep pressure rise due to instantaneous uncontrolled combustion of the fuel that has got accumulated during delay period. The pressure wave hitting piston and cylinder walls produce knocking sound.

DIRECT INJECTION ENGINES – have a single open combustion chamber into which the entire quantity of fuel is injected directly.

DISPERSION OF SPRAY – The divergency of the fuel spray which helps distribution of fuel droplets in air as uniform as possible.

DRIBBLING – Unatomized fuel running from the fuel nozzle.

DUAL FUEL ENGINE – An engine that uses an air gas mixture which is being ignited by a small quantity of fuel oil injected at the end of the compression process.

DURATION OF FUEL INJECTION – The crank angle during which fuel is injected into the engine cylinder. Usually as load increases this duration has to be increased.

EFFECTIVE STROKE OF PLUNGER – The distance from the point of closure of the ports by the plunger top to the point of opening of the spill port by the helical groove on the surface of the plunger. This decides duration and quantity of fuel delivery by the pump.

ENGINE DERATING – Reducing maximum fuel flow to the engine.

FUEL FILTER – A kind of strainer in which there are openings of definite size all over the surface, which retains contaminants in the fuel and permits supply of dust free fuel to the fuel injection system.

FUEL LINE – Thick walled high pressure tubes connecting the delivery end of the fuel injection pump with an injector nozzle located in each of the cylinder head.

FUEL METERING – Measuring and delivering the required amount of fuel for each cycle in accordance with the engine load and delivering the same amount of fuel to each cylinder for each power stroke of the engine.

FUEL PUMP DELIVERY VALVE – assembly relieves the high pressure pipe and maintains a residual pressure in the high pressure pipe. It also reduces the work per cycle in pressurizing the fuel in the system.

FUEL TRANSFER PUMP – A mechanical device used to transfer fuel from the low level fuel tank to the injection pump.

GLOW PLUG – is an electrical heater, which is switched on for quick starting in cold weather. Its heating element protrudes directly into the combustion chamber in DI engines.

GOVERNOR – Mechanism connected to the control rack of the fuel injection pump and thus acts as an intermediate mechanism between the control rack and accelerator pedal.

HOT SMOKE – The smoke that consists of unburned carbon particles (0.5 to 1.0 micron in diameter) and other solid combustion products. This may be light gray to black smoke.

IGNITION LAG – The time interval between the start of injection and start of ignition. Also called DELAY PERIOD.

INDIRECT INJECTION ENGINES – have the combustion space divided into two parts connected by a nozzle or one or more number of orifices. The fuel is injected into the auxiliary chamber. The main chamber is situated in the piston top.

INJECTION LAG – Time interval between the closure of the fuel pump ports by the plunger and the begining of fuel injection by the injector.

INJECTION PUMP – A high variable pressure pump delivering fuel into the combustion chamber.

INJECTION SYSTEM – The components necessary for delivering fuel to the combustion chamber in correct quantity, at the correct time and in a condition satisfactory for efficient combustion.

INJECTION TIMING – Crank angle with respect to TDC at which fuel injection starts, during the compression stroke.

INJECTOR – A device for injecting fuel oil into the combustion chamber of an engine against the pressure of air within the chamber. Also called INJECTION NOZZLE.

MASKED VALVE – An inlet valve which has a mask i.e., a projection, at the rear of the valve head over a part of the periphery so as to admit air in the desired direction.

MAXIMUM SPEED GOVERNOR – limits the maximum speed of operation of a diesel engine.

MECHANICAL INJECTION – Mechanical force pressurizing the metered fuel and causing injection.

METERING FUEL PUMP – A fuel pump delivering a controlled amount of fuel per cycle.

MINIMUM AND MAXIMUM SPEED GOVERNORS – are used predominantly in motor vehicles. The idle and maximum speeds are governed, but not the range in between where the quantity of fuel injected is controlled by the accelerator pedal.

MIXED CYCLE – An engine in which fuel burns partly at constant volume and partly at constant pressure. Sometimes applied to the actual combustion cycle in most high speed diesel engines.

NOZZLE – The component containing the fuel valve and having one or more orifices through which fuel is injected.

OPEN COMBUSTION CHAMBER – A type of diesel combustion chamber in which all the air meant for combustion is confined in one space and combustion of entire fuel takes place within this space. Also called DIRECT INJECTION CHAMBER or QUIESCENT CHAMBER.

OPEN TYPE NOZZLE – A simple spray nozzle open to the cylinder but with a check valve which prevents the high pressure gases in the engine cylinder from passing to the pump.

OPTIMUM INJECTION ADVANCE – Fuel injection timing before TDC which will result in minimum ignition delay.

ORDERLY TURBULENCE – Air motion which is controlled as to direction and velocity.

PENETRATION – The distance through which fuel particles are carried by the kinetic energy imparted to them when they leave the fuel nozzle.

PHYSICAL DELAY PERIOD – The time that elapses between the beginning of fuel injection and the begining of pre-flame reactions.

PILOT INJECTION – is the early injection of a small quantity of fuel to initiate combustion of the injected main fuel, in a diesel engine.

PINTLE TYPE NOZZLE – A closed type fuel nozzle having a projection on the end of the fuel valve which extends into the orifice when the valve is closed.

PRECOMBUSTION CHAMBER – Part of the combustion space located in the cylinder head, into which fuel is injected, and combustion starts here and spreads into the main chamber via the interconnecting orifices.

QUALITY GOVERNING – Power developed is governed by varying the quantity of fuel injected while the quantity of air sucked in is almost the same. The air fuel ratio in the combustion chamber is different at different loads.

RATE OF FUEL INJECTION – Amount of fuel that is injected into the combustion chamber in unit time or in one degree of crank travel.

REENTRANT COMBUSTION CHAMBER – is an open combustion chamber which has a smaller diameter (opening) at the entry than at the middle.

RESIDUAL PRESSURE – The pressure at which the fuel is retained in the fuel line when the injector needle valve and the pump delivery valve are in the closed position.

SAC VOLUME – is the dead volume between the nozzle seat and the end of the spray holes, in a multi hole injector.

SEMI DIESEL – A diesel which utilizes injection of fuel, but also uses electric spark ignition.

SMOKE – is nothing but the carbon particles suspended in the exhaust gases.
It may be blue smoke, black smoke and white smoke.

SODIUM COOLED VALVE – A valve designed to allow the stem and head to be made hollow and partially filled with metallic sodium for better cooling.

SOLID INJECTION SYSTEM – The system which injects only the metered quantity of fuel by means of a pumping device. Also called AIRLESS INJECTION SYSTEM.

SQUISH – Radial inward flow of air from the annular space above the piston; into the combustion chamber cavity during the compression stroke of the piston.

SQUISH AREA – The area confined to the cylinder head and flat surface of the piston when on compression stroke, which causes squish.

SQUISH HEIGHT – refers to the clearance between the piston top and cylinder head, at TDC. This is reduced to a minimum consistent with manufacturing capabilities and operational aspects.

SUCTION SWIRL – Rotary motion imparted to the air during suction by admitting air into the engine cylinder in a tangential direction.

SUPER CHARGING – Process of admitting into the engine cylinder, a charge larger in quantity (i.e., weight) than what the cylinder would contain due to regular suction stroke i.e., by natural aspiration.

SURFACE FILTER – Fuel filter similar to a sieve, consists of a number of discrete holes and pores, through a single layer of material.

SWIRL – Rotation of mass of air as it enters the engine cylinder. This is one form of turbulence.

SWIRL COMBUSTION CHAMBER – Part of the combustion space, spherical or cylindrical in shape, located in the cylinder head, in which vigorous swirl is created and into which fuel is injected and combustion starts and spreads into the space above the piston.

SWIRL RATIO – is the ratio of (air) swirl speed in the combustion chamber to engine speed.

TIMING MARK (injection) – The mark made on the vibration damper or flywheel, used to check injection timing.

TURBULENCE – Violent swirling motion. Fuel injection produces some turbulence. Additional turbulence is provided by the design features of the combustion chamber.

TURBULENCE CHAMBER – A combustion chamber connected to the cylinder through a throat. Fuel is injected across the chamber and turbulence is produced in the chamber by the air entering during compression.

TWO STAGE COMBUSTION – Combustion occurring in two distinct steps such as in a pre-combustion chamber.

UNCONTROLLED COMBUSTION – is the instantaneous combustion of the fuel that got accumulated in the combustion chamber, at the end of the delay period.

UNIT INJECTOR – A combined fuel injection pump and fuel nozzle.

VALVE CLOSING PRESSURE – is the fuel pressure at which the fuel injector needle valve snaps back on its seat. For the differential valve stem, this is less than the nozzle opening pressure.

VALVE CLOSING ORIFICE NOZZLE – In this nozzle, the needle valve sits directly on the top of the orifice. This prevents any fuel in the sac volume escaping into the cylinder after the valve is closed.

VALVE OPENING PRESSURE – is the fuel pressure at which the needle valve of the injector lifts off its seat.

VARIABLE INJECTION TIMING – Altering the injection timing as the engine speed changes (advancing timing as speed increases), by a set of flywheel weights mounted on the injector pump camshaft, to obtain better performance.

VARIABLE SPEED GOVERNOR – Governs both the idle and maximum speeds as well as the range in between.

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