Ear Type Intake[1]

] Supersonic inlets Supersonic intakes exploit shock waves to decelerate the airflow to a subsonic condition at compressor entry. There are basically two forms of shock waves: 1) Normal shock waves, lie perpendicular to the direction of the flow. These form sharp fronts and shock the flow to subsonic speeds. Microscopically the air molecules smash into the subsonic crowd of molecules like alpha rays. Normal shock waves tend to cause a large drop in stagnation pressure. Basically, the higher the supersonic entry Mach number to a normal shock wave, the lower the subsonic exit Mach number and the stronger the shock (i.e. the greater the loss in stagnation pressure across the shock wave). 2) Conical (3-dimensional) and oblique shock waves (2D) are angled rearwards, like the bow wave on a ship or boat, and radiate from a flow disturbance such as a cone or a ramp. For a given inlet Mach number, they are weaker than the equivalent normal shock wave and, although the flow slows down, it remains supersonic throughout. Conical and oblique shock waves turn the flow, which continues in the new direction, until another flow disturbance is encountered downstream. Note: Comments made regarding 3 dimensional conical shock waves, generally also apply to 2D oblique shock waves. A sharp-lipped version of the pitot intake, described above for subsonic applications, performs quite well at moderate supersonic flight speeds. A detached normal shock wave forms just ahead of the intake lip and 'shocks' the flow down to a subsonic velocity. However, as flight speed increases, the shock wave becomes stronger, causing a larger percentage decrease in stagnation pressure (i.e. poorer pressure recovery). An early US supersonic fighter, the F-100 Super Sabre, used such an intake. An unswept lip generate a shock wave, which is reflected multiple times in the inlet. The more reflections before the flow gets subsonic, the better pressure recovery More advanced supersonic intakes, excluding pitots: a) exploit a combination of conical shock wave/s and a normal shock wave to improve pressure recovery at high supersonic flight speeds. Conical shock wave/s are used to reduce the supersonic Mach number at entry to the normal shock wave, thereby reducing the resultant overall shock losses. b) have a design shock-on-lip flight Mach number, where the conical/oblique shock wave/s intercept the cowl lip, thus enabling the streamtube capture area to equal the intake lip area. However, below the shock-on-lip flight Mach number, the shock wave angle/s are less oblique, causing the streamline approaching the lip to be deflected by the

presence of the cone/ramp. Consequently, the intake capture area is less than the intake lip area, which reduces the intake airflow. Depending on the airflow characteristics of the engine, it may be desirable to lower the ramp angle or move the cone rearwards to refocus the shockwaves onto the cowl lip to maximise intake airflow.

c) are designed to have a normal shock in the ducting downstream of intake lip, so that the flow at compressor/fan entry is always subsonic. However, if the engine is throttled back, there is a reduction in the corrected airflow of the LP compressor/fan, but (at supersonic conditions) the corrected airflow at the intake lip remains constant, because it is determined by the flight Mach number and intake incidence/yaw. This discontinuity is overcome by the normal shock moving to a lower cross-sectional area in the ducting, to decrease the Mach number at entry to the shockwave. This weakens the shockwave, improving the overall intake pressure recovery. So, the absolute airflow stays constant, whilst the corrected airflow at compressor entry falls (because of a higher entry pressure). Excess intake airflow may also be dumped overboard or into the exhaust system, to prevent the conical/oblique shock waves being disturbed by the normal shock being forced too far forward by engine throttling. Many second generation supersonic fighter aircraft featured an inlet cone, which was used to form the conical shock wave. This type of inlet cone is clearly seen at the very front of the English Electric Lightning and MiG-21 aircraft, for example.

The same approach can be used for air intakes mounted at the side of the fuselage, where a half cone serves the same purpose with a semicircular air intake, as seen on the F-104 Starfighter and BAC TSR-2. Some intakes are biconic; that is they feature two conical surfaces: the first cone is supplemented by a second, less oblique, conical surface, which generates an extra conical shockwave, radiating from the junction between the two cones. A biconic intake is usually more efficient than the equivalent conical intake, because the entry Mach number to the normal shock is reduced by the presence of the second conical shock wave. A more sophisticated approach is to angle the intake so that one of its edges forms a ramp. An oblique shockwave will form at the start of the ramp. The Century series of US jets featured a number of variations on this approach, usually with the ramp at the outer vertical edge of the intake which was then angled back inwards towards the fuselage. Typical examples include the Republic F-105 Thunderchief and F-4 Phantom. Later this evolved so that the ramp was at the top horizontal edge rather than the outer vertical edge, with a pronounced angle downwards and rearwards. This approach simplified the construction of the intakes and permitted the use of variable ramps to control the airflow into the engine. Most designs since the early 1960s now feature this style of intake, for example the F-14 Tomcat, Panavia Tornado and Concorde. ELEPHANT EAR - (1) An air intake characterized by twin inlets, one on each side of the fuselage. (2) A type of balanced aileron in which the outer edges are noticeably larger than the control itself. In air intakes the kinetic energy is partially transformed into pressure. The distortion of the flow in front of the engine is due to the non uniformity of the flow in front of the lips, the shape of the diffusor, the development of boundary layer on the walls and sometimes the shock-boundary layer interaction. This distortion has to be reduced to keep a good efficiency of the turbojet. The mass flow needed by the engine has to be provided by the air intake for the overall flight envelope. Thus additional inlets or variable geometry are used for supersonic aircraft and fighter.For supersonic vehicles (aircraft and missile) external flow compression induces a penalty for the cowl drag, so mixed compression air intakes are interesting for high cruise Mach numbers. However in this case, some small perturbations can cause the buzz phenomenon by dynamic effect of the shock displacement near the throat. Some devices have to be developed to prevent this risk (internal diverter, porous wall,...). Twin­intake air­induction systems have been used extensively for jet aircraft operating at subsonic and  supersonic speeds. Such a system utilizes symmetrical twin intakes which join in a common duct at a  station forward of the engine compressor Although this type of system  can give relatively high  efficiency, it is susceptible t o twin­duct instability characterized by inlet flow asymmetry when  operated at reduced mass­flow conditions. The inherent flow asymmetry of twin­inlet systems has been  analyzed i n references 1 and 2 and found t o be associated with the static­pressure characteristics of the  individual ducts. 

..Wind­tunnel observations of twin­duct flow asymmetry .at supersonic speeds indicates that flow 

unsteadiness or r'buzz" can occur simultaneously with flow asymmetry. indicates duct­flow asymmetry 

produces an unbalance of pressure forces on the airplane which leads t o severe aircraft stability and control  problems. Heretofore, wind­tunnel measurements of these forces, knowledge of which  are are necessary t o any analysis of the stability variations involved, have not been reported.  The purpose of t h i s investigation was t o examine the nature of asymmetrical flow i n twin­intake  systems at supersonic speeds and t omeasure the effects on airplane static stability. These measurements  the adverse effects of flow asymmetry on aircraft dynamics as recorded i nflight. Possible methods of  alleviating the unfavorable stability characteristic s we re also investigated .Force and pressure  measurements were obtained for each of three :One model (Model A) was complete twin­duct airplane  configurations. investigated more extensively than the other two. For this model the t e s t Mach numbers  were 1.6, 1.8, 2.0, and 2.35. foot varied from 2 . 4 1 0to1.710for this Mach number range. angle 

of attack was varied from ­2' t o+l5'and angle of sidelip from ­5' t o+7O. of a and at Machnumbers of  2.2 and 2.1, respectively. The Reynolds number per The Models B and C were investigated for slightly  different values .

FUEL-INJECTION: A fuel system that uses no carburetor but sprays fuel either directly into the cylinders or into the intake manifold just ahead of the cylinders. It uses an electronic sensing device to deliver the correct amount into the combustion chamber. Throttle-body injection locates the injector(s) centrally in the throttle-body housing, while port injection allocates at least one injector for each cylinder near its intake port. ... Fuel injection is an electronic system that increases performance and fuel economy because it monitors engine conditions and provides the correct air/fuel mixture based on the engine's demand. Unlike a carburetor, which mixes fuel and air together before loading it into the cylinder intake port, fuel injection injects the fuel directly into the cylinder head enabling more precise control over the quantity used. Eliminates need for a carburetor and the complex, imprecise tuning that goes with it. Fuel injection is a means of

metering fuel into an internal combustion engine. In modern automotive applications, fuel metering is one of several functions performed by an "engine management system". The functional objectives for fuel injection systems can vary. All share the central task of supplying fuel to the combustion process, but it is a design decision how a particular system will be optimized. There are several competing objectives such as: • • • • • • • • • • •

power output fuel efficiency emissions performance ability to accommodate alternative fuels durability reliability driveability and smooth operation initial cost maintenance cost diagnostic capability range of environmental operation

Certain combinations of these goals are conflicting, and it is impractical for a single engine control system to fully optimize all criteria simultaneously. In practice, automotive engineers strive to best satisfy a customer's needs competitively. The modern

digital EFI system is far more capable at optimizing these competing objectives than a carburetor.

[edit] Benefits An engine's air/fuel ratio must be accurately controlled under all operating conditions to achieve the desired engine performance, emissions, driveability, and fuel economy. Modern EFI systems meter fuel very precisely, and when used together with an Exhaust Gas Oxygen Sensor (EGO sensor), they are also very accurate. The advent of digital closed loop fuel control, based on feedback from an EGO sensor, let EFI significantly outperform a carburetor. The two fundamental improvements are: 1. Reduced response time to rapidly changing inputs, e.g., rapid throttle movements. 2. Deliver an accurate and equal mass of fuel to each cylinder of the engine, dramatically improving the cylinder-to-cylinder distribution of the engine. Those two features result in these performance benefits: •

Exhaust Emissions o Significantly reduced "engine out" or "feedgas" emissions (the chemical products of engine combustion). o A reduction in the final tailpipe emissions (≈ 99.9%) resulting from the ability to accurately condition the "feedgas" to make the catalytic converter as effective as possible.

•

General Engine Operation o Smoother function during quick throttle transitions. o Engine starting. o Extreme weather operation. o Reduced maintenance interval. o A slight increase in fuel economy.

•

Power Output o Fuel injection often produces more power than an equivalent carbureted engine. However, fuel injection alone does not increase maximum engine output. Increased airflow is needed to burn more fuel to generate more heat to generate more output. The combustion process converts the fuel's chemical energy into heat energy, whether the fuel arrived via EFI or via a carburetor. Airflow is often improved with fuel injectors, which are much smaller than a carburetor. Their smaller size allow more design freedom to improve the air's path into the engine. In contrast, a carburetor's mounting options are limited because it is larger, it must be carefully oriented with respect to gravity, and it must be

about as far from each of the engine's cylinders. These design constraints generally compromise airflow into the engine

Basic function The process of determining the amount of fuel, and its delivery into the engine, are known as fuel metering. Early injection systems used mechanical methods to meter fuel (non electronic, or mechanical fuel injection). Modern systems are nearly all electronic, and use an electronic solenoid (the injector) to inject the fuel. An electronic engine control unit calculates the mass of fuel to inject. The fuel injector acts as the fuel-dispensing nozzle. It injects liquid fuel directly into the engine's air stream. In almost all cases this requires an external pump. The pump and injector are only two of several components in a complete fuel injection system.

[edit] Functional description A contemporary EFI system comprises a digital computer "engine control module" (ECM) and a number of sensors to measure the engine's operating conditions. The ECM interprets these conditions in order to calculate the amount of fuel, among numerous other tasks. The desired "fuel flow rate" depends on several conditions, with the engine's "air flow rate" being the fundamental factor. The electronic fuel injector is normally closed and opens to flow fuel as long as an electric pulse is applied to the injector. The pulse's duration (pulsewidth) is proportional to the amount of fuel desired. The pulse is applied once per engine cycle, which permits pressurized fuel to flow from the fuel supply line, through the open injector, into the engine's air intake, usually just ahead of the intake valve. Since the nature of fuel injection dispenses fuel in discrete amounts, and since the nature of the 4-stroke-cycle engine has discrete induction (air-intake) events, the ECM calculates fuel in discrete amounts. The injected fuel mass is tailored for each individual induction event. In other words, every induction event, of every cylinder, of the entire engine, is a separate fuel mass calculation, and each injector receives a unique pulsewidth based on that cylinder's fuel requirements. It is necessary to know the mass of air the engine "breathes" during each induction event. This is proportional to the intake manifold's air pressure/temperature, which is proportional to throttle position. The amount of air inducted in each intake event is known as "air-charge", and this can be determined using one of several methods, but this is beyond the scope of this topic The three elemental ingredients for combustion are fuel, air and ignition. However; complete combustion can only occur if the air and fuel is present in the exact stoichiometric ratio, which allows all the carbon and hydrogen from the fuel to combine with all the oxygen in the air, with no undesirable polluting leftovers.

. To achieve stoichiometry, the air mass flow into the engine is measured and multiplied by the stoichiometric air/fuel ratio 14.64:1 (by weight) for gasoline. The required fuel mass that must be injected into the engine is then translated to the required pulse width for the fuel injector. Deviations from stoichiometry are required during non-standard operating conditions such as heavy load, or cold operation, in which case, the mixture ratio can range from 10:1 to 18:1 (for gasoline Combustion instabilities not only result in deterioration of combustor performance that affects the overall propulsion system performance, but also may lead to extensive fatigue and vibration that can reduce the operational life, and may even lead to premature failure. Among the various technologies tried over the past decades, secondary fuel injection has shown promise and ease of retrofit. Research has shown that the timing of secondary fuel injection (with respect to the vortex formation in the combustor flow) has a tremendous impact on the stability enhancement. However, the secondary fuel injection involves additional components and weight, which may affect the overall system performance. It is proposed that a pulsed fuel delivery system is used, and highly energetic secondary fuel is utilized. This will enable a reduction in secondary fuel otherwise required, lead to complete combustion, and increase thermal output. An increased thrust will thus be possible without an increase in the combustor volume, and the specific primary fuel consumption can also be reduced. The secondary fuel can be high energy strained hydrocarbon fuels, such as cubane and benzvalene derivatives or nano metallic particle of aluminum (Alex), boron etc. PHASE I: Identify a suitable high energy secondary fuel, and develop injection scheme for sequential injection. Conduct flow and/or computational studies to understand particle size, distribution and trajectories. PHASE II: Design and fabricate a secondary fuel injection and a simple test combustor or modify an off the shelf combustor (simple liquid fuel engine), and perform pulsed secondary fuel injection studies. Investigate vibration levels, noise and thermal output with and without secondary fuel injection. Validate computational tools for use in Phase III. PHASE III: Install the secondary fuel system in a realistic engine (Government-provided), and perform a full parametric evaluation of thrust performance, vibration and noise, and fuel utilization. Optimize system integration for retrofit, and provide new design criteria.