External and internal combustion

The 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

Internal combusion

Petrol / Gasoline in an ICE

When 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.

Diesel ICE

A 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.

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 engine

The 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.

Source

Free piston linear alternator

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.

Small particles in diesel exhaust

But 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.
Developers have responded to this by improving fuel injection systems and exhaust treatment devices, while fuel makers have responded by improving the composition of the fuel. The improvements seen are best demonstrated by the tightening that has occurred over than last 10 years in the allowable PM emission limits which have reduced by a factor of around 30 for passenger cars, and around 50 for larger vehicles.
Much of the PM reduction has come about from the lowering of fuel sulphur content from a staggering 5000 ppm in the late 1990’s to now less than 10 ppm. This reduction has also enabled use of high-temperature exhaust treatment devices which burn off much of the PM remaining. But herein lies a problem; for these filters to work they must be hot. Short trips typically made-up of school runs and local shopping are not good for these systems. Without the benefit of the high temperature that results from a longer trip, higher emissions result, and even the possibility of filter failure.
For the buyer, assessing the benefits of emissions is made easier by the Green Vehicle Guide which separately weights fuel consumption and exhaust emissions to give an overall vehicle rating. Despite their better fuel consumption, diesel vehicles generally rank lower than petrol equivalents. Source

Hydrogen in an internal combustion engine

When 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)

Ammonia

ammonia-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.

Other fuels

Bio oils from plants ....

Ethanol flexi-fuel engine

The 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.

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).

How DICE technology works

The 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.

Advantages

DICE offers a number of advantages that address current energy challenges:
reduction in CO2 intensity of around 20 – to 30 per cent for black coal and 30 – to 50 per cent for brown coals (depending on whether DICE is used for new or replacement of old coal generation capacity);
high efficiency at small unit size resulting lower capital cost;
suitability for base load, peaking and backup duties;
capable of using a diverse range of fuels including biomass and black and brown coals; and
fast start-up can underpin the integration of renewables in the electricity grid, particularly those which are intermittent such as wind, solar and seasonal biofuels.

Metal powder

It is possible to run an engine on metal powder.

Metals to oxide - boron

Metals 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