Diesel Power Generator II

Friendly guide to diesel power generators, diesel engine, backup power generator & electricity, its basic principles & more by Bowerspower.

Diesel Power Generators are also used in remote villages for power in lieu of connecting to the utility grid.  Major construction costs can be averted.

Power is the rate at which an electrical appliance can consume electrical energy, or the rate at which a generator can produce it. In the UK we are charged for our electricity in terms of energy: the more energy we use, the more we pay. A high-power appliance uses energy more rapidly than a low-power one, and therefore costs more to run.

Power is measured in watts, or in kilowatts. A kilowatt is a thousand watts, and is a more useful figure when dealing with electric fires and heaters. The abbreviations are `W' (for watts) and `kW' (for kilowatts). Note the positions of the capital letters here. It is technically incorrect to abbreviate kilowatts to `KW' (although plenty of people do, including electricity supply companies).

The mathematical symbol for power is `P'.
     If we know the voltage and current in an electrical appliance we can work out its power. It turns out that power (in watts) is equal to the voltage (in volts) multiplied by the current (in amps). In symbols this is:

P = V I

So, taking the lightbulb case again, its current (as we worked out earlier) was 0.5 amps, the voltage is (as ever) 230 volts, so the power is 115 watts (0.5 x 230). I don't think you can buy a 115 W lightbulb, so what current flows in a 100 W lightbulb? We can write the formula above in two other ways:

V = P / I

and

I = P / V

The second of these is what we need: it gives us current (`I') if we know P and V. So the current in the 100 W bulb is (100 / 230) amps, or about 0.43 amps.

Here's another example. What rating of fuse do I need in a plug that supplies an electrical kettle? Let's suppose the kettle has a power rating of 2.5 kW (which is common). Since I = P / V, P is 2500 (watts), and V is 230 (volts), we have I = 2500 / 230, which is about 10.9 amps.

Since plug fuses are only usually only available in ratings of 3, 5, and 13 amps, we need a 13-amp fuse, this being the next rating up from the calculated 10.9 amps. A 5-amp fuse would probably blow quite quickly, but we'll come onto that in a moment.

A lightbulb converts electrical energy into light and heat. A filament bulb is very inefficient, in fact, producing about 50 times more heat than light. In fact all electrical equipment gets hot in use, including wires. The amount of energy that goes into heat can always be calculated if we know the voltage and current, but for electrical cables it's easier to do it a different way. Since we know that V = I R (from above) and that P = V I, then a bit of juggling symbols shows that

P = I² R

or in words: power is given by multiplying the square of the current by the resistance. (The square of anything is that number multiplied by itself).

Let's take an example.
    Suppose an electrical cable had a resistance of 2 ohms. This cable is carrying a current of 13 amps (which is the maximum allowed for a plug-in appliance). How much power is turned into heat by the cable?

     Power is given by the square of the current times the resistance, so in this case is 13 x 13 x 2, which is 338 watts. That's about the same as three lightbulbs. So the electrical cable will get about as hot as three lightbulbs. Apart from being a complete waste of energy (which you're paying for), this may be enough heat to melt the cable, which would be a Bad Thing (especially if it's underground).

This explains why we need fat cables for high-power appliances and can get away with thin cables for low-power ones. Fat cables have lower resistances, and therefore less energy is wasted as heat, and they don't get hot enough to melt.

Is it all right to use fat cables for low-power appliances? Well, it doesn't compromise safety, but it's not very cost-effective. Thick cables are much more expensive than thin ones. Another problem is that thick cables are much harder to work with than thin ones. 

Electric Generator Electrical engineers measure electrical energy in kilowatt-hours. One kilowatt-hour is sufficient energy to power a one kilowatt appliance for one hour. An energy of 100 kilowatt-hours may be consumed by an appliance that takes 100 watts running for 1 hour, or an appliance that takes 1 watt running for 100 hours, or anything in between so long as the time multiplied by the power comes to 100.
    
The electricity bill does not distinguish between high-power and low-power appliances, only the total energy. You will normally be charged a certain amount for each kilowatt-hour of energy, plus a certain fixed amount, in each bill.

Many supply companies are now offering charging schemes that remove the fixed amount (standing charge) which is good news for people who are careful with electricity.
    
Here's an example. Suppose your supply company charges 10 pence per kilowatt hour. How much does it cost to run a 40-amp electric shower for half an hour? Since power is voltage times current, the shower will consume 40 x 230 watts. That's 9200 watts, or 9.2 kilowatts. So it would cost 9.2 times ten pence to run it for one hour, or half that for half an hour. So the total cost is (1/2) x 9.2 x 10 pence, or 46

Rudolf Diesel developed the idea for the diesel engine and obtained the German patent for it in 1892. His goal was to create an engine with high efficiency. Gasoline engines had been invented in 1876 and, especially at that time, were not very efficient.

The main differences between the gasoline engine and the diesel engine are:

A gasoline engine intakes a mixture of gas and air, compresses it and ignites the mixture with a spark. A diesel engine takes in just air, compresses it and then injects fuel into the compressed air. The heat of the compressed air lights the fuel spontaneously.

A gasoline engine compresses at a ratio of 8:1 to 12:1, while a diesel engine compresses at a ratio of 14:1 to as high as 25:1. The higher compression ratio of the diesel engine leads to better efficiency.

Gasoline engines generally use either carburetion, in which the air and fuel is mixed long before the air enters the cylinder, or port fuel injection, in which the fuel is injected just prior to the intake stroke (outside the cylinder). Diesel engines use direct fuel injection -- the diesel fuel is injected directly into the cylinder.

The following animation shows the diesel cycle in action. You can compare it to the animation of the gasoline engine to see the differences: