Four and two strokes engines

Four strokes engine: is an internal combustion engine in which the piston completes four separate strokes which gives the name of the engine, constitute a single thermodynamic cycle. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:

1.   Intake: this stroke of the piston begins at top dead center. The piston descends from the top of the cylinder to the bottom of the cylinder, increasing the volume of the cylinder. A mixture of fuel and air is forced by atmospheric (or greater by some form of air pump) pressure into the cylinder through the intake port.

2.   Compression: with both intake and exhaust valves closed, the piston returns to the top of the cylinder compressing the air or fuel-air mixture into the cylinder head.

3.   Power: this is the start of the second revolution of the cycle. While the piston is close to Top Dead Centre, the compressed air–fuel mixture in a gasoline engine is ignited, by a spark plug in gasoline engines, or which ignites due to the heat generated by compression in a diesel engine. The resulting pressure from the combustion of the compressed fuel-air mixture forces the piston back down toward bottom dead centre.

4.   Exhaust: during the exhaust stroke, the piston once again returns to top dead centre while the exhaust valve is open. This action expels the spent fuel-air mixture through the exhaust valve(s).

Two strokes engine: a two-stroke, or two-cycle, engine is a type of internal combustion engine which completes a power cycle with two strokes (up and down movements) of the piston during only one crankshaft revolution. This is in contrast to a "four-stroke engine", which requires four strokes of the piston to complete a power cycle. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust (or scavenging) functions occurring at the same time.

Two-stroke engines often have a high power-to-weight ratio, usually in a narrow range of rotational speeds called the "power band". Compared to four-stroke engines, two-stroke engines have a greatly reduced number of moving parts, and so can be more compact and significantly lighter.

Differences:

- Two-stroke engines do not have valves, simplifying their construction. 
- Two-stroke engines fire once every revolution (four-stroke engines fire once every other revolution). This gives two-stroke engines a significant power boost. But at the same time, they contaminate more
- Two-stroke engines are lighter, and cost less to manufacture. 
- Two-stroke engines have the potential for about twice the power in the same size because there are twice as many power strokes per revolution.

- Two-stroke engines don't live as long as four-stroke engines. The lack of a dedicated lubrication system means that the parts of a two-stroke engine wear-out faster. Two-stroke engines require a mix of oil in with the gas to lubricate the crankshaft, connecting rod and cylinder walls.
- Two-stroke oil can be expensive. Mixing ratio is about 4 ounces per gallon of gas (28.349g/3.8L) burning about a gallon of oil every 1,000 miles(0.62km).
- Two-stroke engines do not use fuel efficiently, yielding fewer miles per gallon.
- Two-stroke engines produce more pollution.
From:
-- The combustion of the oil in the gas. The oil makes all two-stroke engines smoky to some extent, and a badly worn two-stroke engine can emit more oily smoke.
-- Each time a new mix of air/fuel is loaded into the combustion chamber, part of it leaks out through the exhaust port.

Hovercrafts

People have been building boats for a thousands of years, but engineers are still finding better ways to carry us over the water. One of the things that slows boats down is the choppy waves brushing underneath them so, if you want to go faster, you need to go over them. How can you make a boat do this? One way is to use a hydrofoil: a kind of underwater wing that makes a boat fly, very slightly, like a plane. Another option is to use a giant fan and ride your boat on a cushion of air. Boats that work this way are called hovercraft (or, in the military, as LCAC, Landing Craft Air Cushion vehicles).

How it works?

The hovercraft is a vehicle that can slide over the surface under it using a jet of air that makes an air cushion. It can go over every regular horizontal surface such as water, snow, sand or ice without being in contact with it. It is considered to be an airplane because of its way of moving on the air. They usually have two or three engines but some of them have just one.

In a hovercraft, a giant centrally mounted fan creates a massive down-draft of air that pushes the hull upward anything from a few centimeters/inches to a couple of meters (5-6 ft). A cushion of air is trapped underneath the craft by a flexible rubber skirt that can bend around obstacles on water or land. Smaller secondary fans mounted on top, and driven either by the same diesel engine (or separate engines), create a backward force that pushes the hovercraft forward. Rudders behind the fans swivel this backward draft of air from side to side to provide steering.

Small "fingers" of rubber attached to the bottom of the skirt improve the seal between the skirt and the waves beneath it. This maintains the cushion of air, keeping the hovercraft above the water and making the ride smoother for passengers.

HISTORY:

In the middle of the 1880s, the British engineer Sir John Thornycroft built a number of prototypes based on the idea of using air between the hull of a boat and water to reduce the resistance, but it did not found practical applications.

In 1952, the British inventor Christopher Cockerell proposed a practical solution, through simple experiments with a vacuum engine and two cylindrical cans showing the operating principle of a vehicle suspended on a cushion of air driven pressure, which makes possible to move on different surfaces. The most significant improvement was the development of a peripheral system jet to maintain the cushion of air under the vehicle. This sustaining air cushion would allow to operate over muddy and watery surfaces as firm ground on.

The British aircraft manufacturer Saunders Roe was the first person to develop a hovercraft able of carrying a person, the SR-N1, which was subjected to several test programs.

The bearing capacity of the boat was improved by adding a containing "skirt" made of rubber or flexible fabric under the hull, in order to contain the air under it and create an effect of "levitation".

The SR-N1 was equipped with a pistons engine, triggering a series of propellers, creating a direct flow on the surface; It was propelled by air expelled back and it could not be able to transport more than its own weight and the two persons weigh. This was one of the main problems for it sold.

The first passenger hovercraft was the Vickers VA-3, which was carrying passengers regularly along the northern coast of the country of Wales. It worked by two turboprops engines, moved by propellers and was led by a rudder.

During the Decade of the 1960s, Saunders Roe developed several designs for passengers, including the SR-N2, also developed by Cockerell, who added inflatable tubes, aeronautical propellers over aeronautic handles and a system of vents cylindrical to the hull to improve the bearing capacity. Later, the SR-N6 was developed, leading 38 passengers built by Saunders Roe and Vickers (which in 1966 join to form the British Hovercraft Corporation)

At the end of the 60s and beginning of the 70s, the French engineer Jean Bertin developed a hovercraft train called Aero train. Its prototype I-80 established the world speed record for an air cushion vehicle on dry land, wich had an average speed of 417.6 km/h and a maximum of 430 km/h.

In 1970, the largest english hovercraft were the best ones, the model SR-N4, which had four Proteus engines of Rolls Royce; they were driven on the “Canal de la Mancha”.

In the year 2000 the service was interrupted, after years of competing with the traditional boats, catamarans and the Eurotunnel; the reasons were the high cost of maintenance,  the fuel, and the lack of sponsorship State, which at that time was dedicated to large fleets in Europe .

The commercial success of hovercraft was dampened by rapid increases in the cost of the fuel, at the end of the 60's and 70's, what made the conflict in the Middle East; by the introduction of alternative ships, as the catamaran waves borers (marketed as Seacat in Great Britain), which use less fuel and can do almost everything that makes a hovercraft on water. However, elsewhere in the world has continued to develop the technology of the hovercrafts for military and civilian purposes ( the USSR and  the USA developed their own vehicles Hover giant, capable of carrying military arsenal under any weather conditions and in any field of battle), hovercraft practically disappeared from the British coasts, for being reintroduced as lifeguards, lifeboats by the Royal National institution of life boats.

Nowadays, the development of the kevlar and other polymers had made build transports of similar performance with innovative construction techniques and low operating costs such as the hydrofoils, catamarans, the trimarans and the seaplanes, as large as big as a Jumbo, which use the soil effect.

             

Hybrid Cars

On television, in the press, in large ads in the streets or roads... we receive every day more advertising of "hybrid cars".  What are? How do they work? What are the advantages? I am curious, so I thought to delve a bit on the issue asking an expert. So I have requested an interview with an engineer from one of the largest companies which at this time are tucked in the promotion of this interesting technology, Pedro Lasso.

Interviewer: First, can you briefly explain what a hybrid car is?

Pedro: Hybrid cars are a type of vehicle that uses the combination of two motors: one is electric and the other uses fossil fuel (mixture of the conventional and innovative).  This combines an engine of internal combustion with one or more electric motors and an extra battery that takes care of storing the electric power. The proper functioning of the vehicle will be charging the battery, especially when braking and slowing down.  Thus it can decrease emissions of polluting gases into the atmosphere and, at the same time, a good performance of the vehicle can be obtained.

Fig.1. Engine of a hybrid car: combustion engine left. Between this and the string, the generator. On the right, the electric motor

Interviewer: When hybrid cars appear?

Although until 1997 the first hybrid car was no produced in series (the Toyota Prius arrived in Europe in 2000),   one century before (in 1899) Henri Pieper would have developed the first hybrid vehicle of petro-electrical transmission in the world, and in 1900 Ferdinand Porsche developed a series hybrid using two engines, the wheel hub motor and a combustion generator to provide electrical power, establishing two speed records. And in 1978/79 David Arthurs, an electrical engineer from Springdale, Arkansas, developed the regenerative braking hybrid, allowing you to recharge the battery using the energy of braking.

The most recent and used models are based on patent engineer Victor Wouk.

Interviewer: What is the difference between an electric and a hybrid vehicle?

An electric car works 100% with electricity from a battery pack that is recharged when plugged into an electrical outlet. On the other hand the hybrid uses an electric motor, but also other of fossil fuel. The electric car is therefore more eco-friendly, but has a very limited autonomy.

Interviewer: What types of hybrid cars are now on the market?

At least we can speak mainly of the following types:

·         The conventional hybrids that combine a gasoline combustion engine associated with an electric motor. In this type we can include most of the hybrids sold today. These models are capable of storing electricity generated in braking and deceleration in the extra battery. This type of hybrids can operate in mode 100% electric at specific times, as for example in the exit of a garage, or in some sections of town provided that speed will not exceed 40 - 60 km/h.

·         In this line also have started to appear on the market the cars that combine a diesel engine with an electric motor.

·         Most recent are plug-in hybrids: batteries can be charged in a conventional plug, on an external power source (mains), with increasing autonomy in electric mode which will already be raising up to 50 km. These plug-in electric vehicles or plug-in are becoming more common.

Interviewer: What are the advantages of hybrid cars?

There are many advantages of hybrid cars:

• They generate less pollution than conventional cars: reduction of pollutant emissions and lower noise pollution since the hybrid car engine is much quieter than the conventional.
• They more efficiently use energy generated. For example, many hybrid systems allow to collect and reuse the energy generated in braking into electricity thanks to the so-called regenerative brakes: This allows you to get a greater autonomy than the simple electric cars
• There are also economic benefits: saving fuel and official aid (reduction of taxes or subsidies for the purchase)

Interviewer: But it will also have disadvantages? Or not?

Yes, it also has some disadvantages. For example, are more expensive than conventional ones, although the difference is amortized soon, thanks to fuel economy. More energy is consumed for its manufacture and pollution is greater than in the production of e a purely petrol or diesel vehicle. In addition, the materials used for the manufacture of batteries - nickel, among others - can be more harmful against the environment. The hybrid car has difficulty when it comes to repair any breakdown or simply make you a review.

Interviewer: Any ideas for the future?

It is clear that fossil fuels will not last forever. It is also clear that our planet is suffering the consequences of polluting substance abuse. That is why we must find alternatives, and one of them, although still is a significant way to go, is that of hybrid cars. Every day they are developing  more, every day they are more efficient, every day are less polluting--, so undoubtedly today are a good choice.

https://www.youtube.com/watch?t=62&v=CLGygbCr3sg

http://www.hybridcars.com/beijing-removes-rush-hour-limitations-for-electric-cars/

http://www.alternative-energy-news.info/ge-hybrid-tugboats/

https://www.youtube.com/watch?v=EvT9ZwOMRoo

Hidden motors in professional cycling bikes? Technological doping?

The suspicion that professional cyclist use small motors hidden in theis bikes as a kind of'technological doping' has spread in recent years.

Suspicions have grown to produce strange circumstances. There are some well known cases, as Swiss Fabian Cancellara, holder of six world titles in races and time trial Olympic champion in Beijing 2008.  In a race in 2010 he repeated strange movements to press a button near his right brake:  whenever he repeated the suspicious movement, there was a importan change of speed.

               https://www.youtube.com/watch?v=8Nd13ARuvVE

Or the Canadian Hesjedal in the Vuelta a España 2014, when after a tumble the bicycle was still moving on the road while trying to retrieve the cyclist.

               https://www.youtube.com/watch?v=hIlmtQKLMUg

Electric bicycles

Electric bikes (as used in the BICIMAD program Madrid City Council) are "pedal-assist" bicycles, engines do not replace the human effort, but to complement it. So they have the same legal consideration of bicycle, otherwise it would be mopeds. In Spain must meet the following requirements:

               • Have a 250 watt motor nominal power, with assistance up to 25 km / h.

               • The engine is only active while pedaling.

               • Having two brakes (front / rear) and rear reflective.

               • To be authorized for distribution by the Ministry of Industry.

As we said electric bikes require, like normal bicycles, the cyclist pedals move through their own efforts. What elements make up the electrical system? Basically consist of battery, electric motor and pedal sensor that activates the controller.They can also have a screen to bring assistance at various levels and may even bring an accelerator that allows the bike to work as bike without pedaling. In this case it handles cutting out the signal from the engine as soon as the emergency brakes are pressed.
In the market today you may easily acquire these electric bikes or grab a kit to convert regular bike into an electric bike. They may even be practically invisible and silent kits, as well as easily installable, although prices are still high.
For example the Gruber Assit Kit, composed of a button thumbnail, the electronic control that fits into the seat tube, battery (which can provide up to 70 minutes of pedaling assistance) with its charger and engine 200 watts, with a wheel free and connected to the crankshaft through a bevel gear (if the cyclist does not pedal, the bicycle acts as a normal bicycle). The whole kit weighs only 900 grams and can be completely hidden, except the on / off button that sits discreetly at the end of the bar.

Invisible kits for professional cyclists

They say that there are workshops that are installing this hidden engine for professional cyclists, and has come to light even the name of some engineers working discreetly preparing these devices (eg the Hungarian Istvan Varjas who gave an interview to French newspaper L'Equipe). 

Even in recent years, technological advances have made ​​them completely silent and undetectable by mechanics. It is said that can have the size of a USB stick and be hidden in the wheel hubs.

In 2011 the International Cycling Union (UCI) vetoed the propulsion different to the lower muscle 'train'. Electric propulsion in professional sport was banned. So far it has failed to show anything but suspicions are there and have been growing at the pace of advances in the miniaturization of new electric motors designed as support for users of bicycles. In fact only a few days ago, at the end of a stage of the Giro of Italy, UCI made a control surprise of the bikes used by three of the main corridors, including  Spanish Alberto Contador.

The shadow of electronic doping threatens to professional cycling.