Repsol YPF

Electricity generation

For applications that require an electrical supply and are not connected to the network, or for those that need an alternative form of generation other than the network supply for cases of emergency, the energy needed is produced by an electrical power unit, consisting basically of a stationary internal combustion engine which moves an alternator.

Electrical power units are equipped with petrol, gas-oil, natural gas or LPG-fuelled engines. Here, we will discuss the latter type.

Low output

When the electrical demand is very low (approximately up to 10 kVA), electrical power units with petrol-fuelled engines tend to be used, although they can be transformed in order to use propane gas as a fuel, either from bottles or tanks, with bottled gas being the most commonly used. These engines are suitable for emergency generators in industry, construction, public works, quarries, agriculture, stockbreeding, hotels, hospitals, discotheques, sports centres, etc.

The adaptation of a petrol engine to propane gas entails the addition of the relevant fuel lines, from the tank or LPG bottle to the engine, and an evaporation system. The most significant advantages of using propane in these engines are:

• The mixture of propane (in gaseous form) and air is more homogeneous than that of petrol (in liquid form) and air.
  
• Nearer to perfect combustion, leading to greater engine performance and a lower consumption of calories per kW.
  
• Reduction in carbon deposits caused by imperfect combustion.
  
• Less deterioration of lubricating oils, as, with petrol and gas-oil, the mineral components of the fuel attack the lubricant.
  
• Better load distribution in the cylinders, greater regularity in the starting torque and better idling speed.
  
• Better quality of exhaust gases compared with liquid fuels: reductions of 48-83% in low CO emissions, 30-58% in nonburned substances, 4-18% in CO2, 10% in low NOx and, lastly, the absence of acidic sulphur components. 

Medium-high output

For electrical demands of over 10 kVA, above all when the continuous production of electricity is required, the LPG-fuelled electrical power units being used should possess qualities similar to those of diesel engines, some of which are transformed into propane engines.

This type of engine is suitable for small industries, hotel and catering establishments, houses, country houses, mountain refuges, campsites, public works, etc.
The main characteristics of these propane-fuelled electrical power units are:

• Robustness.
• Long life span in order to withstand many hours in operation (usually continuous).
• Low revolution speed (1500 r.p.m.). In general, low and medium power engines use natural aspiration and those with greater power are turbocharged, meaning that they use an air compressor driven by a small turbine running on the exhaust gases. In the case of propane engines, turbocharging provides disadvantages, given propane's low methane index, as high pressures can cause knocking.

Turbocharged engines provide a greater power output for the same level of consumption. However, in order to achieve this greater efficiency, the hot air must cool down at the outlet of the turbocompressor, and therefore an independent cooling system is necessary to supply water at a lower temperature than would normally be provided in engine cooling systems.