Trunk pistons

Trunk pistons are long, relative to their diameter. They act as both piston and also as a cylindrical crosshead. As the connecting rod is angled for part of its rotation, there is also a side force that reacts along the side of the piston against the cylinder wall. A longer piston helps to support this.

Trunk pistons have been a common design of piston since the early days of the reciprocating internal combustion engine. They were used for both petrol and diesel engines, although high speed engines have now adopted the lighter weight slipper piston.

A characteristic of most trunk pistons, particularly for diesel engines, is that they have a groove for an oil ring below the gudgeon pin, not just the rings between the gudgeon pin and crown.

The name 'trunk piston' derives from the trunk engine, an early design of marine steam engine. To make these more compact, they avoided the steam engine's usual piston rod and separate crosshead and were instead the first engine design to place the gudgeon pin directly within the piston. Otherwise these trunk engine pistons bore little resemblance to the trunk piston: they were of extremely large diameter and were double-acting. Their 'trunk' was a narrow cylinder placed mounted in the centre of this piston. Media related to trunk pistons at Wikimedia Commons

The regimes of lubrication

As the load increases on the contacting surfaces three distinct situations can be observed with respect to the mode of lubrication, which are called regimes of lubrication:

• Fluid film lubrication is the lubrication regime in which through viscous forces the load is fully supported by the lubricant within the space or gap between the parts in motion relative to one another (the lubricated conjunction) and solid–solid contact is avoided.
  • Hydrostatic lubrication is when an external pressure is applied to the lubricant in the bearing, to maintain the fluid lubricant film where it would otherwise be squeezed out.
  • Hydrodynamic lubrication is where the motion of the contacting surfaces, and the exact design of the bearing is used to pump lubricant around the bearing to maintain the lubricating film. This design of bearing may wear when started, stopped or reversed, as the lubricant film breaks down.

• Elastohydrodynamic lubrication: Mostly for nonconforming surfaces or higher load conditions, the bodies suffer elastic strains at the contact. Such strain creates a load-bearing area, which provides an almost parallel gap for the fluid to flow through. Much as in hydrodynamic lubrication, the motion of the contacting bodies generates a flow induced pressure, which acts as the bearing force over the contact area. In such high pressure regimes, the viscosity of the fluid may rise considerably. At full elastohydrodynamic lubrication the generated lubricant film completely separates the surfaces. Contact between raised solid features, or asperities, can occur, leading to a mixed-lubrication or boundary lubrication regime.

• Boundary lubrication (also called boundary film lubrication): The bodies come into closer contact at their asperities; the heat developed by the local pressures causes a condition which is called stick-slip and some asperities break off. At the elevated temperature and pressure conditions chemically reactive constituents of the lubricant react with the contact surface forming a highly resistant tenacious layer, or film on the moving solid surfaces (boundary film) which is capable of supporting the load and major wear or breakdown is avoided. Boundary lubrication is also defined as that regime in which the load is carried by the surface asperities rather than by the lubricant.

Besides supporting the load the lubricant may have to perform other functions as well, for instance it may cool the contact areas and remove wear products. While carrying out these functions the lubricant is constantly replaced from the contact areas either by the relative movement (hydrodynamics) or by externally induced forces.

Lubrication is required for correct operation of mechanical systems pistons, pumps, bearings, turbines, cutting tools, etc. where without lubrication the pressure between the surfaces in close proximity would generate enough heat for rapid surface damage which in a coarsened condition may literally weld the surfaces together, causing seizure.

In some applications, such as piston engines, the film between the piston and the cylinder wall also seals the combustion chamber, preventing combustion gases from escaping into the crankcase.

Diesel Oxidation Catalyst (DOC)

For compression-ignition, the most commonly used catalytic converter is the Diesel Oxidation Catalyst (DOC). This catalyst uses O₂ (oxygen) in the exhaust gas stream to convert CO (carbon monoxide) to CO₂ (carbon dioxide) and HC (hydrocarbons) to H₂O (water) and CO₂. These converters often operate at 90 percent efficiency, virtually eliminating diesel odor and helping to reduce visible particulates. These catalysts are not active for NO_x reduction because any reductant present would react first with the high concentration of O₂ in diesel exhaust gas.

Reduction in NO_x emissions from compression-ignition engines has previously been addressed by the addition of exhaust gas to incoming air charge, known as EGR. In 2010, most light-duty diesel manufacturers in the U.S. added catalytic systems to their vehicles to meet new federal emissions requirements. There are two techniques that have been developed for the catalytic reduction of NO_x emissions under lean exhaust conditions - (SCR) and the lean NO_x trap or NOx. Instead of precious metal-containing NOx adsorbers, most manufacturers selected base-metal SCR systems that use a reagent such an ammonia to reduce the NO_x into nitrogen. Ammonia is supplied to the catalyst system by the injection of urea into the exhaust, which then undergoes thermal decomposition and hydrolysis into ammonia. One trademark product of urea solution, also referred to as Diesel Exhaust Fluid (DEF), is adblue

 diesel exhaust contains relatively high levels of particulate matter (soot), consisting in large part of elemental carbon. Catalytic converters cannot clean up elemental carbon, though they do remove up to 90 percent of the soluble organic fraction, so particulates are cleaned up by a soot trap or (DPF). Historically, a DPF consists of a Cordierite or Silicon Carbide substrate with a geometry that forces the exhaust flow through the substrate walls, leaving behind trapped soot particles. Contemporary DPFs can be manufactured from a variety of rare metals that provide superior performance (at a greater expense). As the amount of soot trapped on the DPF increases, so does the back pressure in the exhaust system. Periodic regenerations (high temperature excursions) are required to initiate combustion of the trapped soot and thereby reducing the exhaust back pressure. The amount of soot loaded on the DPF prior to regeneration may also be limited to prevent extreme exotherms from damaging the trap during regeneration. In the U.S., all on-road light, medium and heavy-duty vehicles powered by diesel and built after 1 January 2007, must meet diesel particulate emission limits that means they effectively have to be equipped with a 2-Way catalytic converter and a diesel particulate filter. Note that this applies only to the diesel engine used in the vehicle. As long as the engine was manufactured before 1 January 2007, the vehicle is not required to have the DPF system. This led to an inventory runup by engine manufacturers in late 2006 so they could continue selling pre-DPF vehicles well into 2007.

Angular contact of ball bearing

An angular contact ball bearing uses axially asymmetric races. An axial load passes in a straight line through the bearing, whereas a radial load takes an oblique path that tends to want to separate the races axially. So the angle of contact on the inner race is the same as that on the outer race. Angular contact bearings better support "combined loads" (loading in both the radial and axial directions) and the contact angle of the bearing should be matched to the relative proportions of each. The larger the contact angle (typically in the range 10 to 45 degrees), the higher the axial load supported, but the lower the radial load. In high speed applications, such as turbines, jet engines, and dentistry equipment, the centrifugal forces generated by the balls changes the contact angle at the inner and outer race. Ceramics such as silicon nitride are now regularly used in such applications due to their low density (40% of steel). These materials significantly reduce centrifugal force and function well in high temperature environments. They also tend to wear in a similar way to bearing steel—rather than cracking or shattering like glass or porcelain.

Most bicycles use angular-contact bearings in the headsets because the forces on these bearings are in both the radial and axial dire

HAPPY CHRISTMAS

Faith makes all things possible,
Hope makes all things work,
Love makes all things beautiful,
May you have all the three for this Christmas.
MERRY CHRISTMAS!

Field regulation

Automotive alternators require a voltage regulator which operates by modulating the small field current to produce a constant voltage at the battery terminals. Early designs (c.1960s-1970s) used a discrete device mounted elsewhere in the vehicle. Intermediate designs (c.1970s-1990s) incorporated the voltage regulator into the alternator housing. Modern designs do away with the voltage regulator altogether; voltage regulation is now a function of the (ECU). The field current is much smaller than the output current of the alternator; for example, a 70 A alternator may need only 7 A of field current. The field current is supplied to the rotor windings by slip rings. The low current and relatively smooth slip rings ensure greater reliability and longer life than that obtained by a DC generator with its commutator and higher current being passed through its brushes.

The field windings are supplied power from the battery via the ignition switch and regulator. A parallel circuit supplies the "charge" warning indicator and is earthed via the regulator.(which is why the indicator is on when the ignition is on but the engine is not running). Once the engine is running and the alternator is generating power, a diode feeds the field current from the alternator main output equalizing the voltage across the warning indicator which goes off. The wire supplying the field current is often referred to as the "exciter" wire. The drawback of this arrangement is that if the warning lamp burns out or the "exciter" wire is disconnected, no current reaches the field windings and the alternator will not generate power. Some warning indicator circuits are equipped with a resistor in parallel with the lamp that permit excitation current to flow if the warning lamp burns out. The driver should check that the warning indicator is on when the engine is stopped; otherwise, there might not be any indication of a failure of the belt which may also drive the cooling water pump. Some alternators will self-excite when the engine reaches a certain speed.

Older automobiles with minimal lighting may have had an alternator capable of producing only 30 A. Typical passenger car and light truck alternators are rated around 50-70 A, though higher ratings are becoming more common, especially as there is more load on the vehicle's electrical system with air conditioning, electric power steering and other electrical systems. Very large alternators used on buses, heavy equipment or emergency vehicles may produce 300 A. Semi-trucks usually have alternators which output 140 A. Very large alternators may be water-cooled or oil-cooled.

In recent years, alternator regulators are linked to the vehicle's computer system and various factors including air temperature obtained from the intake air temperature sensor, battery temperature sensor and engine load are evaluated in adjusting the voltage supplied by the alternator.

Efficiency of automotive alternators is limited by fan cooling loss, bearing loss, iron loss, copper loss, and the voltage drop in the diode bridges. At partial load efficiency is between 50-62% depending on the size of alternator and varies with alternator speed. This is similar to very small high-performance permanent magnet alternators, such as those used for bicycle lighting systems, which achieve an efficiency around 60%. Larger permanent magnet alternators can achieve higher efficiencies. Large AC generators used in power stations run at carefully controlled speeds and have no constraints on size or weight. They have much higher efficiencies, as high as 98%.

Automobile air conditioning

Automobile air conditioning systems cool the occupants of a vehicle in hot weather, and have come into wide use from the late twentieth century. air conditioners use significant power; on the other hand the drag of a car with closed windows is less than if the windows are open tocool the occupants. There has been much debate on the effect of air conditioning on the fuel efficiency of a vehicle. Factors such as wind resistance, aerodynamics and engine power and weight have to be factored into finding the true variance between using the air conditioning system and not using it when estimating the actual fuel mileage. Other factors on the impact on the engine and an overall engine heat increase can have an impact on the cooling system of the vehicle.

History

A company in New York City in the United States, first offered installation of air conditioning for cars in 1933. Most of their customers operated limousines and luxury cars.

The packard motor car company was the first automobile manufacturer to offer an air conditioning unit into its cars, beginning in 1939. These air conditioners were manufactured by Bishop and Babcock Co, of Cleveland Ohio. The "Bishop and Babcock Weather Conditioner" also incorporated a heater. Cars ordered with the new "Weather Conditioner" were shipped from Packard's East Grand Boulevard facility to the B&B factory where the conversion was performed. Once complete, the car was shipped to a local dealer where the customer would take delivery.

There were many reasons why this early air conditioner unit was unsuccessful: 1) The main evaporator and blower system took up half of the trunk space. (This problem would go away as trunks became larger in the post-war period.) 2) The system was less efficient than those that would follow in the post-war years. 3) It had no temperature thermostat or shut-off mechanism other than switching the blower off. (Cold air would still enter the car with any movement as the drive belt was continuously connected to the compressor--later systems would use electrically operated clutches to remedy this problem.) 4) The several feet of plumbing going back and forth between the engine compartment and trunk proved unreliable in service. 5) Finally, the biggest reason this early system failed was that it cost US $274.00 (equivalent to $4,544 today) an enormous amount of money in post-depression/pre-war America.

Packard fully warranted and supported this conversion, and marketed it well. However, given the limitations above, it was unsuccessful. Subsequently, the option was discontinued after 1941.

Chrysler Airtemp

The 1953 chrysler imperial was the first production car in twelve years to actually have automobile air conditioning, following tentative experiments by packard in 1940 and cadillac in 1941. walter p. chrysler had seen to the invention of  airtemp air conditioning back in the 1930s for the chrysler building, and had ostensibly offered it on cars in 1941-42, and again in 1951-52, but none are known to have been sold in the latter form until the 1953 model year. In actually installing optional Airtemp air conditioning units to its Imperials in 1953, chrysler beat Cadillac, buick and old mobile which added air conditioning as an option in the 1953 model year.

Airtemp was more sophisticated and efficient than the complicated rival air conditioners of 1953. It recirculated, rather than merely cooled, the air inside the vehicle, and it was also the highest capacity unit available on an automobile. It was also simple to operate, with a single switch on the dashboard marked with low, medium, and high positions, which the driver selected as desired. The system was capable of cooling a Chrysler from 120 degrees to 85 degrees in about two minutes, and of completely eliminating humidity, dust, pollen and tobacco smoke at the same time. Since it relied on fresh air, and drew in sixty percent more of it than any contemporary system, Airtemp avoided the staleness associated with automotive air conditioning at the time. It was silent and unobtrusive. Instead of plastic tubes mounted on the package shelf as on GM and on other cars, small ducts directed cool air toward the ceiling of the car where it filtered down around the passengers instead of blowing directly on them, a feature that modern cars have lost.