External and internal combustionThe external combustion engine ICE, is one where the heat source is outside the vessel containing the expanding gases or vapour. For example a steam engine with a fire under the boiling water. The boiler can be fire tube, or water tube. A steam engine is usually fire tube. The internal combustion engine has the heat source inside the piston. The first proposed internal combustion engine was based on a cannon, first with gunpowder, then with gas (CO and H2) being ignited to push a piston up the barrel. 1680, Dutch scientist Huygens created the first “internal combustion engine”. Powered by gunpowder, "It could lift 7 or 8 small boys in the air". Source |
External combustion |
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Petrol / Gasoline in an ICEWhen petrol / gasoline is used, a spark plug ignites the compressed petrol vapour. It expands and pushes the piston away, which in turn pushes and rotates a crankshaft. This crankshaft in turn pushes other pistons into their compression phase. A flywheel smooths out the motion. |
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Diesel ICEA diesel is slightly different. It has no spark plug, but relies on air compression alone to heat the fuel to ignition temperature. The piston has a higher compression ratio so the gases can be compressed to a higher temperature and are therefore more efficient. (Carnot efficiency). Diesel fuel is less easily flammable.
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The efficiency of any heat engine depends on the temperature difference between the hot and cold end. The higher the temperature difference, the higher the efficiency. So diesels are more efficient because they run at higher temperatures. They use 2/3 the fuel of petrol engines. However they produce fine particles that kill people. Diesels can run on almost any fuel. Diesel fuel is a heavier crude oil fraction than diesel so it contains more carbon than petrol. More carbon means more production of the greenhouse gas carbon dioxide (CO₂), but this increase is mitigated by lower fuel consumption. |
Free piston engineThe higher the compression ratio, the higher the temperature and the efficency. In a normal piston motor the compression ratio is limited by the wear in bearings etc. A clever way around this is to have the piston in a cylinder with no connecting rod but with fuel ignition at each end. The fuel is ignited sending the piston back to the other end where another fuel explosion sends it back again. The energy is taken out as electricity. The piston has rare earth super magnets and these generate electricity is coils in the cylinder walls. Instead of a rotating magnet, this one goes back and forth. The motor is called a free piston linear alternator. The compression ratio is controllable allowing a large variety of fuels to be used. |
Free piston linear alternator |
When used in an E10 blend, greenhouse gases (compared to unleaded petrol) are lower by 1.7 % (from wheat) to 5.1 % (C-molasses using co-generation).
LS: Low Sulfur, ULS: Ultra Low Sulfur, CNG: Compressed Natural Gas (Methane) Fischer-Tropsh, FT, is a process for converting methane etc into liquid fuel. FT liquids from biomas is similar in emissions to ethanol from wood. |
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Small particles in diesel exhaustBut there is more than just carbon dioxide leaving the exhaust. Diesel vehicles are renowned for the black smoke they produce. The particulate matter (PM) that makes up this smoke constitutes a minute fraction of the fuel burned, but its reduction remains one of the major challenges facing these engines. |
Green vehicle guide |
1,200,000 people dying of air pollution related lung disease in India and China each year, the imperative to clean up emissions is arguably more important than simply saving money on diesel fuel costs. | |
Hydrogen in an internal combustion engineWhen used in diesel engines, hydrogen needs to be compressed for injection into the cylinder. But doing so can consume up to 15 percent of its output power See Hydrogen fuelled vehicles (This website) |
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Ammoniaammonia-based fuels offer a great potential for universal use. The present disadvantage is that pure ammonia is not suitable for use in high-speed engines. Its flame speed is too low. However, ammonia can be doped by environmentally friendly chemical additives, and thus be compatible in high-speed engines. Ammonia is already compatible in other energy devices, such as low-speed engines and fuel cells. It is an abundantly produced chemical used in industry and agriculture. Source. In the 1940s in Belgium when diesel was hard to get, the bus fleet was run on ammonia. This rocket was powered by ammonia and set speed and altitude records in the 1960s. |
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Other fuelsBio oils from plants .... Ethanol flexi-fuel engineThe flexi-fuel vehicle can use a mix of ethanol or petrol up to 85 % ethanol. This type of vehicle is in common use in Brazil, with around 70 % of vehicles capable of operating on a mix of petrol and ethanol. The cost of production of these vehicles is in the order of $100 more expensive than a standard petrol vehicle — but the standard vehicles cannot be cheaply converted. |
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Direct Injection Coal Engines (DICE)Direct Injection Coal Engine (DICE) is a large diesel engine modified to use coal-water fuels. Used in relatively smaller applications, these highly efficient heat engines (>50%) could support the development of renewables by providing cost effective and efficient backup and provide benefits through decentralisation of generation plant (through reduced power transmission losses). The energy penalty for CO2 capture can be reduced by utilising waste heat in the capture process from the coal engine (Wibberley, 2007). |
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How DICE technology worksThe technology involves converting carbon sources such as coal or biomass into a water-based slurry called micronised refined carbon (MRC). MRC looks like black water-based paint (see picture above). It can use fuel with water content such as plants, peat, or brown coal. This fuel is then directly injected into a large specially adapted diesel engine, called DICE. The fuel burns in a similar manner to heavy diesel fuel, to produce intense temperature and pressure in the engine, which provides highly efficient power to turn electrical generators. |
AdvantagesDICE offers a number of advantages that address current energy challenges: |
Metal powderIt is possible to run an engine on metal powder. Metals to oxide - boronMetals such as Boron can be oxidised to give off heat and run an engine. Then the metal oxide formed can be reduced back to metal in the power station. The oxide however will weigh 2.5 times more than the metal and this would need to be returned for reprocessing. So, interesting but difficult to find a practical use. |
6B + 3O2 ---> 2B3O3 6x10.8 + 3x32 ---> 160.8 |
The green vehicle guide is an excellent Australian government website on vehicle emissions |