Posts Tagged ‘transport’

How a steam loco differs from diesel-electric loco?

2013/09/23

A diesel-electric (DE) loco is a constant power machine. We know that, Power = Force x Velocity. This means, when hauling heavy loads (especially on an uphill), a DE loco can increase draw bar pull by reducing speed. This also shows why most shunting locos are DE locos as they need to haul heavy load but at low speed.

 

However, due to the way a steam loco is designed (i.e. its boiler, piston and other mechanisms), a steam loco behaves as a constant force machine up to cruising speed (usually around 25 MPH or 40 km/h). Beyond that, a steam loco behaves like a constant power machine like a DE loco.

 

This difference is crucial. For a steam loco to haul heavy load (or on an uphill), if it can’t deliver enough draw bar pull, it has no way to increase the force like a DE loco, because for steam loco, force is constant at low speed. So, a steam loco won’t be able to climb a slope like a DE loco. It will literally run out of puff under such circumstance. However, once a steam loco has crossed its cruising speed, it will have no problem pulling heavy trains as it behaves in same way as DE loco i.e. constant power loco.

 

There are obviously other differences between these two types of locos. A DE loco is more thermally efficient than a steam loco. The later requires far more maintenance than the former and needs more crews to operate them.

 

No wonder, due to these reasons, most of old steam locos have been replaced by DE locos in all but heritage routes. Please note that a pure electric loco will also behave similarly as of a DE loco.

 

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Air-cooled vs water cooled engine

2012/08/01

Most likely your modern car has a water-cooled engine. When an internal combustion engine operates, it creates high amount of heat. Unless there is a mechanism to dissipate the heat, it will damage the engine components. In modern automobile engines, a coolant system is used to keep the engine cool. Usually a chemical coolant is used (although named water cooled, water is not used anymore now as coolant) within a sealed system (you rarely need to top up). The cooling system creates a jacket outside the engine. It also keep the engine in constant temperature. The proof is your car’s temperature gauge which usually stays halfway to H and C mark.

In air-cooled engine, air is used to cool the engine down. Thus, it does not require radiator and cooling system – which makes the whole engine a lot simpler. It uses radiator fins (easy to see in motorcycles) which are used to cool the engine. But there are drawbacks too. Unless there is steady flow of air, the engine may get overheat quickly. They are also very noisy as the radiators fins vibrate when engine is in operation.

Air-cooled engines are used mainly in motorcycles, some 3-wheels (like India’s Bajaj autorickshaws), some cars (classic VW Beetle, old Porsches etc.) and some propeller aircrafts.

For aircrafts, they are not a big problem. Unlike a car, an aircraft does not get stuck in traffic jams. Aircraft engines operate within their 80-100% RPM range most of the time and due to high speed cruising plenty of air pass over the radiator fins to keep them cool. This also explains why old propeller aircrafts with such engine sound so loud.

But problem might happen in air-cooled car engines! If the car is stuck in traffic or moving slowly over extended period of time, the engine may overheat (which may lead to seizure of engine).  On the other hand, they are quite good at cold weather condition as chance of overheating is lower.

 

Why auto stop start is modern cars?

2012/07/16

Many new cars of today feature auto stop start feature. This is also known as Intelligent Stop and Go and similar names.

Cars with this feature, turns of engine as soon as you stop and take your foot off the clutch. Then as soon as you press clutch again to engage the gear, it switches on the engine.

Manufacturers do this because they claim it saves fuel while waiting in traffic.  This also allows them to quote higher fuel economy figures and CO2 emission (on which most cars are taxed nowadays). This makes these cars statistically more attractive (because of lower fuel consumption and tax) to the buyers.

On the other hand, many drivers find it as a psychological challenge. It also requires a stronger (thus more expensive) battery and starter motor. So how much money is saved at the end (for drivers) is open to debate.

Fortunately, if you do not like this feature, it can usually be turned off via a switch on dashboard.

As of now, automatic cars do not have this feature but in future this may be offered in autos as well.

 

Why auto rickshaw is not used as personal transport?

2012/06/10

Auto rickshaws are ubiquitous low cost public transport in India and few other countries in SE Asia.

It is positioned in the market between two wheelers and cars. But strangely enough these vehicles are never used as personal transport! It might seem intuitive that those can afford these but not cars could be using as personal transports but that idea never caught. There is no clear explanation for this but usually it is assumed that people in India assume this as low status vehicle. One does not like to be seen driving this. Those who drive auto rickshaws for living are considered not being up to any better quality jobs (even though they earn moderate amount of money as per Indian standard).

Those who can afford cars won’t buy autos because they offer very poor ride quality, comfort and safety kits compared to proper cars. In fact, some people consider autos as worst of both worlds. They are not comfortable as cars and not cheap and agile enough like two wheelers.

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