LNG - the 'smart' fuel

The British name for Gasoline in its original early full sense was petroleum distillate¹. Heat is imparted to a mix of crude oils to fracture or ‘crack’ the chemical bonds. This releases the volatile compounds that are distilled off to create fuels that are most commonly used in transportation, such as petrol, diesel and kerosene.

Additives are mixed in to create blends to conform to government regulations, which require amelioration of their toxicity when burnt in a reciprocating or turbine engines. These are all added costs to the basic distilled product to allow it to be used in engines.

A major problem is cleanliness of all the internal working components to allow the reciprocating CI and SI engines to run correctly over an extended period of time between service intervals. It is well known that diesel engines, in particular, have detergent additives in the lubricating oils to dissolve diesel by-products of combustion deposited inside the engine. The diesel particulate problem of soot emissions has still not been fully solved, with special emphasis on nano-soot particles, which cause respiratory problems in those living in close proximity to roadways. Expensive after-treatment techniques have been incorporated, but these do not completely alleviate the issue of nano-soot paticulates.

After using considerable energy to heat the crude to break down those loose chemical bonds, to distill out the higher volatiles we use for fuels, the crude oil is forced to cool rapidly to individually condense out its various constituents. What happens to all the energy that is used to heat up the crude? It is dissipated as waste heat energy.

It is then rapidly carried away by the cooling distillation process and either radiated or vented to the atmosphere. This is after it has been used to boil-off and separate the volatiles. This is a poor use of energy, to create a usable fuel. It is a wasteful energy practice, which is recovered at the pump through the consumer’s pocket.

LNG

The argument often put forward is that it is expensive to liquefy natural gas, and that is only partly and simplistically true. However the product you get in return, in one single step of liquefaction, is a purer fuel to burn and does not need any other additives. This would keep a number of CI and SI engines much cleaner and thus operating at higher peak performance levels over a longer period of time, without expensive maintenance and adjustments (or resorting to costly additives and after-treatments that are not required to maintain a consistent performance level).

Diesel/gasoline are complex chemistry, single energy availability fuels. In comparison, cryogenically cooled fuels, such as LNG or liquid hydrogen, are ‘smart’ fuels as they retain two types of energy (or dual energy availability fuels).

That is because when natural gas is cooled and stored the energy is retained, unlike the distillation of crude oil which leaks off the energy used to ‘crack’ the crude oil energy to ambient. Distillation fuels tend to lie dormant in a simple single skin tank, which boils off a certain amount as temperatures rise and fall in the surrounding ambient air or sun load upon the storage container. This can be most readily recognised as the standing vertical vent pipes at gas stations with their slight shimmering haze bleeding off the raw high volatile hydrocarbons that leak to the atmosphere.

However, in the case of LNG, the liquefaction energy is still kept within the fuel. This cryogenic secondary energy source can be harnessed for useful work. This liquefaction energy can be used for a dual symbiotic process. In an electrical hybrid powertrain, a closed loop energy system can be designed whereby it can cool the electronic components to make them operate more efficiently and thus increase their power density [power/weight] or to downsize them in the finished design. The cryogenic cooling will also aid durability by the efficient targeted removal of heat from critical components. This waste heat energy creates a power type that is more readily usable by slower traction speed motors or the energy storage devices. Similarly, the central control unit is analogous to a cars ECU distribution circuitry, which can lose efficiency by operating at high temperatures. It can also have its efficiency and durability improved operating in the -100°C range.

One can visualise all the heat generated from computers, circuit boards, and individual chips that are cooled by fans.The waste heat from all these devices working at near cryogenic temperatures are now imparted back to the fuel, to be used to regasify the LNG to a gas molecular state. In the case of the Hybine Propulsion Systems® design, this is a small efficient turbine to provide a fuel that is readily able to burn and release its primary hydrocarbon energy to create power in the form of electrical energy from its attached generator to drive the vehicle. This forms a more efficient closed loop energy use process.

¹ This term is now more commonly used for the class of solvents produced in the fracturing and distillation of crude oil.

 Written by Ian Sharp, Hybine Propulsion Systems, USA.  Edited by Callum O'Reilly

Read the article online at: https://www.lngindustry.com/small-scale-lng/24042014/lng_smart_fuel_471/