SUPERCRITICAL FUEL INJECTION-A PROMISING TECHNOLOGY FOR IMPROVED FUEL EFFICIENCY SEMINAR REPORT

Seminar Report 2015-16

1 Ilahia College of Engg & Tech Department of Mechanical Engineering

CHAPTER 1

INTRODUCTION

Advanced diesel and gasoline engines, and alternative fuels, are really at the middle of

everything. For the next 30 years, these are more ‘classical power trains’ will dominate in

industry. The traditional four stroke Otto cycle engine piston engine only has a thermal efficiency

of 25-30 percent; there is clearly still plenty of room for improvement. While most of the green

automobile attention in recent years has been focused on electrification, liquid fuels still have

about 100 times the energy density of today’s best lithium-ion batteries, a difference that probably

won’t change significantly any time in the near future. With that in mind, there is still plenty of

effort being expended on improving the humble internal combustion engine. These efforts range

from completely different structures like Eco Motors opposed piston opposed cylinder (OPOC) to

new combustion processes such as homogeneous charge compression ignition (HCCI).

One of the most interesting combustion related developments comes from a transonic

combustion. In 2007, a company was claiming it could get an ICE vehicle to 100 mpg. The

transonic system isn’t really a radical departure from what we have today on engines. The system

has fuel injectors, a common rail, a fuel pump, and a control system. The system could be readily

integrated in to existing engines; company anticipates production of the concept in 2015 time

frame. It is a fact that liquid fuels are going to be there for a long time more and more they’re

going to be from alternative sources. That’s why we need to optimize the propulsion system for

those liquid fuels. The heart of transonic technology is a new fuel delivery system. To get the

liquid fuel into a supercritical state before injecting into the combustion chamber.

Traditionally, matter has been thought of as having three states liquid, solid, gas and any

given material can exist in one of those at any point in time depending on the temperature and

pressure. Fuels like gasoline and diesel generally only burn after they are vaporized. . The injector

may operate on a wide range of liquid fuels including gasoline, diesel and various bio fuels. The

injector fire at room pressure and up to the practical compression limit of IC engines.



CHAPTER 2

LITERATURE SURVEY

De Boer, C., Bonar, G., Sasaki, S., and Shetty, S.

Application of Supercritical Gasoline Injection to a Direct Injection Spark Ignition Engine for

Particulate Reduction (2013)

Investigations using novel fuel injection equipment, which allows fuel injection at highly

elevated temperatures, were made to demonstrate the potential for improved mixture formation

and exhaust particulate emission mitigation. Tests were carried out on a single cylinder gasoline

spark ignition engine with direct fuel injection and operating in both homogeneous and stratified

charge modes. Detailed measurements of the combustion characteristics, thermal efficiency and

exhaust emissions were made. Particular attention was paid to particulate emission; measurements

including smoke (FSN), particulate mass and particle count were made. Tests were carried out

over a wide range of engine speed and load conditions to demonstrate that combustion

performance is generally maintained. Particulate mass reduction in excess of 50% and particle

count reduction of more than 90% were measured. Additional tests were carried out to

characterize the performance of heated sprays using an optical pressure vessel under engine

operating conditions over a range of fuel temperatures. The optical data was used to map spray

geometry, dynamics and quality.

Zoldak, P., de Boer, C., and Shetty, S.

Transonic Combustion - Supercritical Gasoline Combustion Operating Range Extension for Low

Emissions and High Thermal Efficiency (2012)

The TSCi™ combustion process exhibits similarities with HCCI, LTC, PCCI and RCCI

with high indicated thermal efficiencies (greater than 45%) and simultaneous reduction of NOx

and PM at high EGR levels. The use of EGR at low and medium loads has shown a strong

impact on NOx without compromising particulate emissions control of combustion phasing,

whereas the TSCi™ combustion process, due to its partially premixed and partially stratified

mixture preparation, is not limited in the same manner.



For the TSCi™ process the use of copious EGR levels have demonstrated to be effective

in reducing NOx and cylinder pressure rise rates while maintaining start of combustion control and

low soot emissions at light load conditions. The test results presented in this paper are from

extensive single-cylinder engine studies. The results demonstrate the operating range capability of

the TSCi™ process at low load without EGR, medium load with use of EGR, and high speed low

load with EGR. The results further the technical understanding of the performance of the TSCi™

process into operating regions previously unattained. The impact on thermal efficiency, NOx, PM,

hydrocarbons (HC), and carbon monoxide (CO), as well as the ability to control pressure rise

rates, combustion stability, combustion duration and ignition delay will be presented. The impact

of SOI, Boost, fuel temperature and intake temperature on the supercritical combustion process

are also reported.

De Boer, C., Chang, J., and Shetty, S.

Transonic Combustion - A Novel Injection-Ignition System for Improved Gasoline Engine

Efficiency (2010)

Supercritical fuel achieves rapid mixing with the contents of the cylinder and after a short

delay period spontaneous ignition occurs at multiple locations. Multiple ignition sites and rapid

combustion combine to result in high rates of heat release and high cycle efficiency. The

injection-ignition process is independent from the overall air/fuel ratio contained in the cylinder

and thus allows the engine to operate un-throttled. Additionally, the stratified nature of the charge

under part load conditions reduces heat loss to the surrounding surfaces, resulting in further

efficiency improvements. The short combustion delay angles allow for the injection timing to be

such that the ignition and combustion events take place after TDC. This late injection timing

results in a fundamental advantage in that all work resulting from heat release produces positive

work on the piston. Other advantages are the elimination of droplet burning and increased

combustion stability that results from multiple ignition sources. Engine test results are presented

over a range of speed, load and operating conditions to show fuel consumption, emission and

combustion characteristics from initial injector and combustion system designs.



Hossain, K., Qiu, J., Shetty, S., Zoldak, P.

Transonic Combustion: Model Development and Validation in the Context of a Pressure

Chamber(2012)

This paper focuses on the validation efforts for supercritical n-heptane injected at different

pressures. The comparison metrics encompassed fluid jet penetration, ignition delay and lift-off

length. A reduced chemistry model for n-heptane was developed for the supercritical regime. The

reduction process included sensitivity studies, to match ignition delay timing to results from

shock-tube experiments available in literature. The chemistry model was implemented in a

transient three-dimensional CFD simulation. The simulation results were then validated against

data from the pressure chamber and the penetration rate, ignition delay and lift-off-length

compared well with the experimental data.

Panchasara, H. V

Spray charecteristics and combustion perfomance of unheated and pre-heated Liquid Biofuels

(2010)

Preheat the fuel to reduce the kinematic viscosity and thereby making it possible to

atomize in combustion systems. Kinematic viscosity is an important physical property affecting

pressure drop in the fuel line as well as the fuel atomization in the combustor. High fuel viscosity

can result in excessive pressure drop and produce spray with large droplets, which deteriorates the

combustion performance. The emissions decreased significantly; by a factor of 2 to 3 for CO and

6 to 15 for NOx for a given fuel inlet temperature. Comparative study of liquid fuel composition

and their thermo physical properties shows that the blending of high viscosity fuel with low

viscosity fuel would be the simple viable option to improve the fuel spray characteristics required

to effectively atomize the fuel to reduce emissions in liquid fuel combustion. Physical properties

such as kinematic viscosity and volatility of the bio-oils were improved by blending them with a

low viscosity and high volatility fuel such as diesel. For a given ALR, the CO emissions

decreased by 1 to 2 ppm and NOx emissions reduced by 20 ppm with increase in fuel inlet

temperature with increase in ALR.



CHAPTER 3

THE TSCITM ENGINE

The TSCiTM engine is based on the principle of the supercritical fuel injection. In

TSCiTM engine, ignition system is removed and redesigned the fuel injection. Transonic

Combustion is a venture capital and private equity funded start-up with facilities in Los Angeles

and Detroit. Founded in 2006, its focus is to develop and commercialize fundamentally new fuel

injection technologies that enable conventional internal combustion automotive engines to run at

ultra-high efficiency. By operating high compression engines that incorporate precise ignition

timing with carefully minimized waste heat generation, Transonic Combustion may have a

“transformational” technology—one that can achieve double efficiency compared to current

gasoline powered vehicles in urban driving. In turn, the company’s products also may

significantly reduce fossil fuel consumption and GHG emissions. Transonic patented product is

its TSCi™ fuel injection system that utilizes supercritical fuel, enabling significant improvements

in fuel consumption Employing supercritical fuel in automotive power trains is being pioneered

independently by Transonic according to Brian Ahlborn, the company’s CEO.

Supercritical fuels have unusual physical properties that facilitate short ignition delay, fast

combustion, and low thermal energy loss. This result in highly efficient air-fuel ratios over the

full range of engine conditions from stoichiometric air-fuel ratios of 14.7:1 at full power to lean

80:1 air-fuel ratios at cruise, down to 150:1 at engine idle. Many existing gasoline engines can

only achieve around 20:1. The implication is clear Transonic’s proposition may facilitate a

significantly more efficient combustion process than is currently employed. While the

intellectual property is understandably proprietary, Transonic Combustion’s unique feature is that

it injects fuel in a different manner. Fuel is raised to a supercritical state and injected during the

combustion process with more precise timing, meaning Transonic’s process uses substantially

less fuel than conventional systems. The supercritical fuel is directly injected as a "non-liquid

fluid" rather than “droplets” into the combustion chamber very near the top of the piston stroke.

This ensures that the heat of combustion is efficiently released only during the power stroke, thus

allowing for more degrees of freedom in engine management. .



A new combustion process has been developed based on the patented concept of

injection-ignition known as Transonic Combustion or TSCi™; this combustion process is based

on the direct injection of fuel into the cylinder as a supercritical fluid. Supercritical fuel achieves

rapid mixing with the contents of the cylinder and after a short delay period spontaneous ignition

occurs at multiple locations. Multiple ignition sites and rapid combustion combine to result in

high rates of heat release and high cycle efficiency. The injection-ignition process is independent

from the overall air/fuel ratio contained in the cylinder and thus allows the engine to operate un-

throttled. Additionally, the stratified nature of the charge under part load conditions reduces heat

loss to the surrounding surfaces, resulting in further efficiency improvements. The short

combustion delay angles allow for the injection timing to be such that the ignition and

combustion events take place after TDC. This late injection timing results in a fundamental

advantage in that all work resulting from heat release produces positive work on the piston.

Other advantages are the elimination of droplet burning and increased combustion stability that

results from multiple ignition sources. Engine test results are presented over a range of speed,

load and operating conditions to show fuel consumption, emission and combustion

characteristics from initial injector and combustion system designs. The results are correlated

with thermo-dynamic modeling and comparisons are made with contemporary engines.

Fig 3.1: TSCiTM fuel injection system



CHAPTER 4

SUPERCRITICAL FUEL AND INJECTION SYSTEM

A comparison of standard direct injection of liquid fuel and transonic’s novel

supercritical injection process (as viewed through an optical engine fitted with a quartz window)

shows that the new TSCi fuel delivery system does not create fuel droplets. Throughout the

history of internal combustion engine, engineers have boosted cylinder compression to extract

more mechanical energy from a given fuel-air charge. The extra pressure enhances the mixing

and vaporization of the injected droplets before burning. Transonic combustion is focusing on

raising not only the fuel mixture’s pressure but also its temperature. In fact, is to generate a little

known, intermediate state of matter also called supercritical fluid (SC), which could markedly

increase the fuel efficiency of next generation power plants while reducing their exhaust

emissions.

Transonic’s proprietary TSCi fuel-injection systems do not produce fuel droplets as

conventional fuel delivery units do. The supercritical condition of the fuel injected into a

cylinder by a TSCi system means that the fuel mixes rapidly with the intake air which enables

better control of the location and timing of the combustion process. The novel SC injection

system, called as “almost drop in” units include “a GDI type,” common rail system that

incorporates a metal oxide catalyst that breaks fuel molecules down into simpler hydrocarbons

chains, and a precision, high speed (piezoelectric) injector whose resistance heated pin places

the fuel in a supercritical state as it enters the cylinder. If we doubled the fuel efficiency numbers

in dynamometers tests of gas engine installed with the SC fuel injection systems. A modified

gasoline engine installed in a 3200 lb (1451 kg) test vehicle, for example, is getting 98 mpg

(41.6 km/L) when running at a steady 50 mph (80 km/h) in the lab. To minimize friction losses,

the transonic engineers have steadily reduced the compression of their test engines to between

20:1 and 16:1, with the possibility of 13:1 for gasoline engines. Fuel conditioning is an emerging

technology based on the discovery that high powered magnets placed in a particular pattern on

fuel feed lines cause the fuel to burn at a higher temperature and more efficiently. Fuel is heated

beyond thermodynamic critical point. Heating is in the presence of a catalyst. Fuel injection is

by using a specially designed fuel injector.



Fig 4.1: Supercritical fuel injection

The new technology in addition is achieving significant reductions in engine out

emissions. Some test engines reportedly generate only 55-58 g/km of CO2, a figure that is less

than half the fleet average value established by the European Union for 2012. Two automakers

are currently evaluating transonic test engines, with a third negotiating similar trials.

4.1 IGNITION TIMING IS THE KEY

SC fluids have unique properties. For a start, their density is midway between those of a

liquid and gas, about half to 60% that of the liquid. On the other hand, they also feature the

molecular diffusion rates of a gas and so can dissolve substances that are usually tough to place

in solution. Additionally, a SC fluid has a very low surface tension. This enables quicker

mixing, and it exhibits catalytic activity that is two to three orders of magnitude faster than the

purely liquid form of the substance.



If you eliminate the time it takes to vaporize fuel and the heat lost with contact with the

cylinder walls, we could improve the base efficiency of an engine far beyond what would

normally be possible to achieve with. The TSCi system uses supercritical fuel to place most of

the combustion in the hot eddy of gas that forms at the centre of a standard diesel cylinder

chamber. It is been figured that by changing the ignition delay so that that fuel ignited in that

area, the flame can be kept away from contact with the walls, which take heat out the engine. It

was designed to limit combustion to within the first 20 to 30 degrees past top dead centre, to

make full use of mechanical energy created by burning while reducing the heat lost to the

exhaust.

Fig 4.2: Supercritical fuel injection in optical spray vessel

4.2 SWEET SPOT

To minimize friction losses, the transonic engineers have steadily reduced the

compression of their test engines to between 20:1 and 16:1, with the possibility of 13:1 for

gasoline engines. There may be some advantage to going a little higher, but the developers had

tried to keep the fuel system within the range that OEMs understand. The fundamental problem

is that on average about 15% of the energy from the gasoline you put into your tank gets used to

move your car down the road. The rest of the energy is lost to engine and driveline inefficiencies



The engine is where most thermal efficiency loss takes place. Combustion irreversibly

results in large amount of waste heat escaping through the cylinder walls and unrecoverable

exhaust energy. Normal engines runs with rich air to fuel ratios, which also results in fuel being

trapped in the crevice as well as partially combusting near the cylinder walls, this energy loss is

the core of automotive inefficiency. While we explore solutions for a car industry that accounts

for half of the transportation sector’s fuel consumption and greenhouse gas emissions, many

short-term and long term alternatives are being considered, each option has deep implications in

terms of sourcing raw materials, changing automotive power train architectures, revamping

energy infrastructures, and many unknown technological and environmental consequences.

The considerable economic costs to consumers and society must be carefully considered

to pursue the most viable, sustainable solutions. Experts from academia and industry agree that

the technologies required to improve the efficiency of new cars and trucks mainly involve

incremental change to conventional internal combustion engines. According to a recent study,

efficiency improvements of internal combustion engines can reach 30% by 2020 and up to 50%

by 2030. The potential benefits are large and greatly exceed the expected costs of improved fuel

economy. Cutting global average automotive fuel consumption by 50% would reduce emissions

of CO2 by over 1 gig ton a year by 2025 and over 2 gig tons by 2050, resulting in annual savings

of imported oil worth over $300 billion in 2025 and $600 billion in 2050 (oil = $100/barrel). For

consumers, the cost of improved technology for more fuel efficient cars could be recovered by

fuel savings in the first few years of use of a new car. But volatile oil prices create conditions

that influence new car buyers purchase consideration of higher efficiency, higher priced vehicles

that in turn influence product offerings from global car manufacturers. Another study found that

fuel efficiency improvements enabled by advanced combustion technologies of 50% or more for

automotive engines and 25% or more for heavy duty truck engines relative to today’s diesel

truck engines) are possible in the next 10 to 15 years .

The most promising directions for novel combustion strategies for high efficiency, clean

internal combustion engine technology involve combustion of lean or dilute fuel air mixtures

beyond limits that have been reached to date. Local mixture composition is the driving

parameter for ignition, combustion rate and pollutant formation.



Therefore it is crucial to understand and control how fuel, air, and potentially

recirculated exhaust gas are mixed.The potential to improve fuel efficiency with advanced

internal combustion engine technologies is enormous. Transonic’s breakthrough high energy

efficiency, low carbon footprint solution disrupts the stagnant efficiency trajectory of the

internal combustion engine over the past 100 years. Transonic’s lean combustion process utilizes

lean air to fuel ratios that minimize many of thermal efficiency losses from today’s engine

technology. Transonic’s precision controlled fuel injection systems address these issues to

dramatically improve the efficiency and halve the emissions of modern internal combustion

engines.

4.3 THE TRANSONIC COMBUSTION TECHNOLOGY

The transonic technology provides a heated catalyzed fuel injector for dispensing fuel

predominately or substantially, exclusively during the power stroke of an IC engine. This

injector lightly oxidizes the fuel in a supercritical vapour phase via externally applied heat from

an electrical heater or other means. The injector may operate on a wide range of liquid fuels

including gasoline, diesel and various bio fuels. The injector fire at room pressure and up to the

practical compression limit of IC engines. Since the injector may operate independent of spark

ignition or compression ignition, its operation is referred to herein as “injection-ignition”. There

are two major aspects to transonic technology, the fuel preparation and the direct injection

system. The fuel delivery system is an evolution of current direction injection systems that use a

common high pressures (200-300 bar) rail to deliver fuel directly to each combustion chamber

through individually controlled injectors.

According to the transonic, the fuel is catalyzed in the gas phase or supercritical phase

only, using oxygen reduction catalysts. The injector greatly reduces both front end and back end

heat losses within the engine. Ignition occurs in a fast burn zone at high fuel density such that a

leading surface of the fuel is completely burned within several microseconds. In operation, the

fuel injector precisely meters instantly igniting fuel at a predetermined crank angle for optimal

power stroke production.



Fig 4.3: The combustion technology by common rail system

The transonic combustion, engine includes a combustion chamber, wherein the fuel

injector is mounted substantially in the centre of the cylinder head of the combustion chamber.

During operation, a fuel column of hot gas is injected into the combustion chamber, such that a

leading surface of the fuel column auto detonates and the fuel column is radially dispensed into a

swirl pattern mixing with the intake air charge. The combustion chamber provides a lean burn

environment, wherein 0.15 to 5% of the fuel is pre oxidized in the fuel injector by employing

high temperature and pressure. Pre oxidation within the fuel injector may include the use of

surface catalysts disposed on injector chamber walls and oxygen sources including standard

oxygenating agents such as methyl tetra butyl ether (MTBE), ethanol, other octane and cetane

boosters, and other fuel oxygenator agents, pre oxidation may further comprise a small amount

of additional oxygen taken from air or from recirculated exhaust gas. Cheiky's aim, in fact, is to

generate a little- known, intermediate state of matter—a so-called supercritical (SC) fluid—

which he and his co- workers at Camarillo, CA-based Transonic Combustion believe could

markedly increase the fuel efficiency of next-generation power plants while reducing their

exhaust emissions.



Transonic’s proprietary TSCi fuel-injection systems do not produce fuel droplets as

conventional fuel delivery units do, according to Mike Rocke, Vice President of Marketing and

Business Development. The supercritical condition of the fuel injected into a cylinder by a TSCi

system means that the fuel mixes rapidly with the intake air which enables better control of the

location and timing of the combustion process. The novel SC injection systems, which “almost

drop-in” units, include “a GDI-type,” common-rail system that incorporates a metal-oxide

catalyst that breaks fuel molecules down into simpler hydrocarbon chains, and a precision, high-

speed (piezoelectric) injector whose resistance-heated pin places the fuel in a supercritical state

as it enters the cylinder.

Company engineers have doubled the fuel efficiency numbers in dynamometer tests of

gas engines fitted with the company’s prototype SC fuel-injection systems. A modified gasoline

engine installed in a 3200-lb (1451-kg) test vehicle, for example, is getting 98 mpg (41.6 km/L)

when running at a steady 50 mph (80 km/h) in the lab. The 48-employee firm is finalizing a

development engine for a test fleet of from 10 to 100 vehicles, while trying to find a partner with

whom to manufacture and market TSCi systems by 2014. “A supercritical fluid is basically a

fourth state of matter that’s part way between a gas and liquid,” said Michael Frick, Vice

President for Engineering. A substance goes supercritical when it is heated beyond a certain

thermodynamic critical point so that it refuses to liquefy no matter how much pressure is

applied. SC fluids have unique properties. For a start, their density is midway between those of a

liquid and gas, about half to 60% that of the liquid. On the other hand, they also feature the

molecular diffusion rates of a gas and so can dissolve substances that are usually tough to place

in solution.



CHAPTER 5

SUPERCRITICAL FLUID TECHNOLOGY

Many new research studies and technologies are making strides to improve methods of

treating hazardous waste. Researchers are examining many diverse topics for treating chemical

contamination of water and soils. Some of the most recent treatment processes include reverse

osmosis, ozone/peroxide/UV treatment, zero-valent metal reduction, and supercritical fluid

oxidation.

Fluids may exist as liquids, gases and supercritical fluids. Supercritical fluids exist at

high temperatures and pressures and exhibit properties between those of a gas and liquid phase.

Supercritical fluid oxidation is a rapid process that completely oxidizes organic contaminates.

This process requires creating a supercritical fluid, as the name implies, to act as a solvent to

organics and initiates inorganic precipitation. The following discussion will cover the

background and process description and design considerations of supercritical fluid oxidation. A

supercritical fluid is a material at an elevated temperature and pressure that has properties

between those of a gas and liquid and is a substance with a temperature above its critical

temperature and critical pressure. Specifically, the supercritical fluid has densities approaching

those of a liquid phase and diffusivities and viscosities approaching those of a gas phase. The

temperature and pressure required to initiate supercritical properties will differ from material to

material. Viewing the temperature-pressure phase diagram of water or CO2, the ranges at a given

temperature and pressure will exhibit liquid, solid, gas, or supercritical properties. From the

phase diagram, the critical point of the material is shown as the highest temperature and

pressure, which the vapour and liquid are in equilibrium. Within the supercritical region, phase

changes from liquid to vapour occurs gradually. The supercritical region differs from the other

regions in the phase diagram because phase changes occur instantaneously at pressures and

temperatures lower than the critical point (e.g., at the triple point). The duration that the injector

is open (called the pulse width) is proportional to the amount of fuel delivered to the cylinder.



A table which shows the supercritical properties of various fluids below:

Table 5.1 Supercritical Properties for Various Solvents

Once supercritical properties are obtained, organics within the waste stream can either be

removed or destroyed. Removal occurs when an organic waste stream meets a supercritical

fluid. Organics are known to have high solubility in supercritical fluid thus partitioning from the

contaminate inflow. Once the supercritical fluid dissolves the organics, removal of the waste

from the supercritical fluid is accomplished by either reducing the pressure or temperature.

Reducing the temperature or pressure will then decrease the solubility of the organics in

supercritical fluid thus creating a concentrated extract Pressure reduction typically occurs by

passing the flow through a pressure reduction valve. Once supercritical properties are obtained,

organics within the waste stream can either be removed or destroyed. Removal occurs when an

organic waste stream meets a supercritical fluid. Organics are known to have high solubility in

supercritical fluid thus partitioning from the contaminate inflow. Once the supercritical fluid

dissolves the organics, removal of the waste from the supercritical fluid is accomplished by

either reducing the pressure or temperature.

Reducing the temperature or pressure will then decrease the solubility of the organics in

supercritical fluid thus creating a concentrated extract Pressure reduction typically occurs by

passing the flow through a pressure reduction valve. Temperature reduction can occur by

passing the flow by a heat exchanger that is effective in the recycling process to reheat the fluid

to the supercritical state.



In supercritical fluid oxidation the organic compound is destroyed rather than removed.

In normal environmental oxidation processes, molecular oxygen takes so long to oxidize an

organic compound at ambient temperatures and pressures that it is considered non-reactive.

However, when air is brought to supercritical conditions, the oxidation potential is vastly

increased (Watts, 1998). With the conditions for oxidation potential increased and the ability of

the supercritical fluid to contain all of the organics, the destruction of organics occurs rapidly.

LaGrega indicated that with the proper conditions (temperature = 600 -650oC) the residence or

reactor detention time can be less than one minute with 99.9999% removal efficiencies. From

bench scale studies, various compounds have yielded specific efficiencies, temperatures, and

time to obtain destruction. Under supercritical conditions, the inorganic compounds are

influenced. At ambient temperature and pressure, the dielectric constant is high thus producing

high inorganic solubility. Under supercritical conditions the dielectric constant decreases with

increasing temperature which then decreases the solubility of inorganic compounds. The

reaction of inorganic compounds to supercritical properties is the inverse to that of hydrocarbon

compounds in that the later increases in solubility with increasing temperature.

5.1 APPLICATIONS

In the past, practical applications of supercritical fluids were limited to the food

processing and extraction industry. Supercritical fluids put to use for extraction and separations

began in the 1970’s and 1980’s. Each year tens of millions of kilograms of the world’s coffee

and tea is decaffeinated using supercritical carbon dioxide. In Germany for example, most

decaffeinated coffee is produced using this method. Not only does this result in a cleaner

industrial process, but it also ensures that the final product is purer because it has not been

exposed to harmful solvents. Environmental applications of supercritical fluids are seen in both

pollution prevention and remediation of wastes. Supercritical fluids provide an environmentally

friendly alternative for solvents used in industrial applications. One of the properties of

supercritical fluids is their excellent ability to dissolve other substances. For example, CO2 is

currently being used to replace harmful hazardous solvents and acts as a reaction medium for

materials processing. CO2 can be removed from the environment, used as an environmentally

friendly solvent, and returned as CO2.



Solubility of greases and oils is very high in supercritical CO2 and no residues remain

after cleaning. Another use in industry is textile dyeing. Industry is developing CO2 soluble

dyes that will eliminate dyed wastewater as a hazardous waste. Supercritical fluids are

important additions to remediation efforts. The solubility behavior of Naphthalene in

Supercritical Carbon Dioxide is shown in figure 4 below. This curve is a general representation

of the behavior of most compounds dissolving in supercritical fluids. Supercritical CO2 also

acts as a solvent to leach metals from solutions, soils and other solids. Another application of

supercritical CO2 is recovery of uranium from aqueous solutions generated in the reprocessing

of nuclear fuels. Supercritical water acts as an excellent solvent to remove and reduce wastes. For

example, water when mixed with organics and oxygen, under supercritical conditions, will

greatly reduce the production of NOx and SOx compared with incineration practices. This is

because water is readily miscible with both oxygen and organics and can achieve very high

destruction efficiencies with very short residence times (1min).This technology is also being

considered for the destruction of chemical weapons and stockpiled explosive, as well as the

cleanup of industrial waste streams, municipal waste and used water from naval vessels.

5.2 DESIGN CONSIDERATIONS

Challenges facing this new technology are scaling and corrosion. The byproduct of the

process is a highly corrosive mineral acid. In addition, salts will form is bases are added to

neutralize. The salts formed are insoluble in water under these conditions. Another important

design consideration in the development of supercritical water oxidation is the optimization of

reactor operating temperature and feed preheats temperatures. Increasing temperature or

pressure may favour better oxidation or solvent properties; however cost will increase due to

pumps and heating. However to reduce costs, one may pick a supercritical fluid that has a lower

critical temperature and critical pressure. Finally, these fluids are extremely corrosive to holding

chambers and are flammable under supercritical conditions. Throughout the history of internal

combustion engine, engineers have boosted cylinder compression to extract more mechanical

energy from a given fuel-air charge.



Fig 5.1: The Comparison of Liquid and Supercritical Fluid:

The extra pressure enhances the mixing and vaporization of the injected droplets before

burning. TSCi Fuel Injection achieves lean combustion and super efficiency by running

gasoline, diesel, and advanced bio-renewable fuels on modern diesel engine architectures.

Supercritical fluids have unusual physical properties that Transonic is harnessing for internal

combustion engine efficiency. Supercritical fuel injection facilitates short ignition delay and fast

combustion, precisely controls the combustion that minimizes crevice burn and partial

combustion near the cylinder walls, and prevents droplet diffusion burn. Our engine control

software facilitates extremely fast combustion, enabled by advanced micro processing

technology. Our injection system can also be supplemented by advanced thermal management,

exhaust gas recovery, electronic valves, and advanced combustion chamber geometries.

When people think about reducing gasoline consumption, alternative-fuel and hybrid

cars usually come to mind. A superefficient fuel injector designed to integrate easily into

conventional cars. Unlike standard fuel injectors, the TSCi injector pressurizes and heats

gasoline to 400 degrees Celsius, bringing it to a supercritical state that is partway between liquid

and gas. When the substance enters the combustion chamber, it combusts without a spark and

mixes with air quickly, allowing it to burn more efficiently than the liquid droplets produced by

standard injectors. A Transonic test car the size and weight of a Toyota Prius achieved 64 miles

per gallon at highway speeds, compared with the 48 mpg highway rating on the Prius.



Fig 6.1: T-S Diagram

CHAPTER 6

THEORETICAL ANALYSIS

6.1 ENERGY ANALYSIS

Specific heat capacity at constant pressure, of Octane, Cp = 2.15 kJ/kg.K

It takes 215 kJ of energy to increase the temperature of 1kg of Octane by 100K.

6.2 COMBINED GAS LAW 𝑃𝑃1𝑉𝑉1

𝑇𝑇1=𝑃𝑃2𝑉𝑉2

𝑇𝑇2

It is known that when comparing the same gas in 2 separate environments then the gases

will have the relationship above, where:

• P = Pressure

• V = Volume

• T = Temperature

Thus in a constant volume comparison, increased temperature will result in increased

pressure. The force inside a combustion chamber, and on a piston, is equal to the pressure

exerted by the gas multiplied by the cross-sectional area of the chamber. So there is a direct

correlation between the gas temperature and the performance of the engine.

6.3 COMBUSTION TEMPERATURE

The idealized Carnot heat engine cycle is illustrated

in the temperature-entropy diagram, F.

The work done by that engine is defined by:

𝑊𝑊 = �𝑃𝑃𝑃𝑃𝑉𝑉 = (𝑇𝑇𝐻𝐻 − 𝑇𝑇𝐶𝐶)(𝑆𝑆𝐵𝐵 − 𝑆𝑆𝐴𝐴)

This indicates that the work output increases as the

difference between TH and TC increases. This also

indicates that TC must be kept relatively cold.



6.4 STOCHIOMETRIC COMBUSTION EQUATION

Iso-Octane, C8H18.

C8H18 + (8+18/4)O2 = 8CO2 + (18/2)H2O

C8H18 + 12.5 O2 = 8CO2 + 9H2O

6.5 STOCHIOMETRIC AFR BY MASS

1 molecule of Iso-Octane, C8H18, is composed of 8 atoms of Carbon and 18 atoms of

Hydrogen. In atomic weights, 8 * 12 = 96 for the Carbon, and 18 * 1 = 18 for the Hydrogen; so

the molecular weight of Iso-Octane is 114; 84.2% Carbon and 15.8% Hydrogen.

The stoichiometric combustion equation of C8H18 is exactly:

C8H18 + (8 + 18/4)O2 = 8CO2 + 18/2H2O.

1 mol + (8 + 18/4) moles = (8 + 18/2) moles.

For one mole of fuel C8H18 there is exactly:

(8+18/4) = 12.5 moles of oxygen for complete combustion.

1 mole of C8H18 weighs:

Carbon 12 * 8 + Hydrogen 1 * 18 = 114 grammes.

1 mole of O2 weighs 32 grammes.

Thus 32*12.5 = 400 grammes of O2 to combust one mole of C8H18.

Assuming 20.95% oxygen in air, 3.77 * 12.5 = 47 moles of N2.

47 moles of Nitrogen = 1316 grammes.

Thus, 1.716 kg of air.

Stoichiometric AFR = 1.716 : 0.114 = 15.05:1

C8H18 + 12.5O2 = 8CO2 + 9H2O.



6.6 ADIABATIC FLAME TEMPERATURE

Again, the adiabatic flame temperature had to be obtained from a trial and error solution.

Cp = 1.234 kJ/kg.K for CO2 at 1000 K.

Cp = 1.8723 kJ/kg.K for water vapour. Using these specific heat values,

Fuel temperature, 320K,

8 * (-393,520 -10183 + CpΔT) + 9 * (-241,820 – 10641 + CpΔT) = -211,543.

Where ΔT = (Taf – 47). The specific heats on a molar base are:

Cp, CO2 = Cp.M = (1.234 kJ/kg ⋅ K)(44 kg/kmol) = 54.3 kJ/kmol.K

Cp, H2O = Cp.M = (1.8723 kJ/kg ⋅ K)(18 kg/kmol) = 33.7 kJ/kmol.K

Substituting,

8 * (-393,520 -10183 + CpΔT) + 9 * (-241,820 – 10641 + CpΔT) = -211,543.

(8 * 54.3)ΔT + (9 * 33.7)ΔT = 5,713,316

∆𝐓𝐓 = 𝟓𝟓,𝟕𝟕𝟕𝟕𝟕𝟕,𝟕𝟕𝟕𝟕𝟑𝟑(𝟖𝟖∗𝟓𝟓𝟓𝟓.𝟕𝟕)+(𝟗𝟗∗𝟕𝟕𝟕𝟕.𝟕𝟕)

= 7744.8

Taf = ΔT + 47 = 7744.8 + 47 =~ 7791 ℃

320 K = 47℃. Estimated adiabatic flame temperature,

420 K = 147℃. Estimated adiabatic flame temperature = ~7908 ℃

520 K = 247℃. Estimated adiabatic flame temperature = ~8021 ℃



CHAPTER 7

CFD SIMULATIONS

The software chosen was a Free, Library and Open Source Software (FLOSS)

CFD package named OpenFoam instead of the ANSYS products previously studied. The

reasons for this was; The FLOSS nature of OpenFoam meant that the program and source code

were available to download, gratis. Having the source code was of benefit as the particulars

could be studied and understood as required; and in the future modifications could be made to

any and all aspects of the simulations.

7.1 ENGINE TEST SPECIFICATIONS

Number of tests 3

Initial fuel temperatures 320 K, 420 K, 520 K

Solver engineFoam

Combustion model Weller’s ‘b-Xi two equation’

Based on tutorial kivaTest

Fuel Iso-octane, C8H18

Cylinder volume 0.242 litres

Compression ratio 4.84:1

Engine speed 1500 RPM

Meshing algorithm blockMesh

Table 7.1: Engine test specifications

7.2 SETUP

1. The OpenFoam package version 2.2.2 was used on the Ubuntu distribution of GNU/Linux.

2. The engine combustion tutorial folder named kivaTest was copied to a project directory and

duplicated three times. The folder names chosen were ‘320’, ‘420’, and ‘520’



3. The command ‘Allrun’ was run to commence the simulation using the engineFoam solver.

4. A Clip filter was added to the model

which cuts the cylinder in half allowing a

view of the interior.

5. The view was coloured by temperature

and the temperature scale adjusted from

minimum to maximum values, 298 to

2900.

6. The timeframe for the results was then be

adjusted and viewed a -180 to 60 degrees

ATDC.

7. Animation of the simulation run was

recorded from 0 to 60 degrees ATDC.

8. Steps 1 to 7 were repeated for the 420 and 520 combustion cases.

7.3 SIMULATION RESULTS

7.3.1 Maximum Flame Temperature

The three simulation runs were analyzed at 60 degrees after top dead centre

(ATDC) using the same intensity scale of 298K to 2900K, blue to red. The three result images in

are arranged, 320K, 420K, 520K, top, middle, and bottom.

As can be seen, the intense temperature ranges increase as the initial fuel

temperature increases.

The maximum gas temperature was analyzed from each simulation run and found to be:

• 320K, Maximum temperature of 2620K.



Thus, the maximum flame temperature increase is not a simple addition of initial heat Increase.

The equation for the line is y = 130x + 2490.



These results plot as follows:

Fig 7.2: Maximum flame temperature

7.3.2 Mean Flame Temperature

The mean flame temperature data was gathered from each of the simulations with

the use of a ‘Python Calculator’ filter in ParaView.The graph and the data shows that roughly,

for every 100 K initial heat added there was an average of 15% flame temperature increase. This

indicates ~15% pressure increase, and ~15% force increase for every 100K of heat added over

298K / 25C of Iso-octane.

Fig 7.3: Mean flame temperature



CHAPTER 8

ATOMIZATION MODELS

The atomization model defines the initial conditions for spray computations. It is

considered that a new atomization model may have to be written to conduct future simulations

with support for increased initial temperatures, and supercritical fluid phase. The atomization

model must resolve in detail, the atomization processes and properties, including particle

diameter, and liquid viscosity variations caused by the initial temperature.

OpenFoam has support for 2 atomization models:

• LISA, Linear Instability Sheet Atomisation.

• Blobs Sheet.

The LISA model incorporates the effect of spray swirl by

preserving the angular velocity component of droplets, which are

injected in a circle, and also includes a transition between the

initial solid cone pre-spray and the ensuing hollow cone spray.

These sprays are typically characterized by high atomization efficiencies. With pressure

swirl injectors, the fuel is set into a rotational motion and the resulting centrifugal forces lead to

a formation of a thin liquid film along the injector walls, surrounding an air core at the centre of

the injector. Outside the injection nozzle, the tangential motion of the fuel is transformed into a

radial component and a liquid sheet is formed. This sheet is subject to aerodynamic instabilities

that cause it to break up into ligaments.

The Blobs Sheet model uses the blob method, which is one of the simplest and most

popular approaches to define the injection conditions of droplets. In this approach, it is assumed

that a detailed description of the atomization and breakup processes within the primary breakup

zone of the spray is not required. Spherical droplets with uniform size, 𝐷𝐷𝑝𝑝 = 𝐷𝐷𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛 , are

injected that are subject to aerodynamic induced secondary breakup.



CHAPTER 9

CONCLUSION

If it works as promised, the transonic combustion engine technology would improve fuel

economy by far more than other options, some of which can improve efficiency on the order of

20 percent. It is expected to cost about as much as high end fuel injection systems currently on

the market.The system can run an engine that uses both gas and diesel as well as biofuels, and it

is supposed to create an engine that is 50 percent more efficient than standard engines. About

two years ago Transonic Combustion showed off a demo vehicle with its engine tech that got 64

miles per gallon in highway driving.

More efficient traditional engines could be a lower-cost way to reduce carbon emissions

from cars before electric vehicles develop into any kind of market. Auto companies will also be

looking for more efficient traditional technologies, because fuel standards in the U.S. are set to

rise from 27 miles per gallon today to 54.5 miles per gallon by 2025, thanks to the Obama

administration’s plan.

By eliminating the ignition system and introducing a completely redesigned fuel

injection system, TSCi (Injector-Ignition) realize a 50% increase in efficiency. With the

influence of supercritical fluid enhances a complete combustion and there by increases engine

efficiency and reduces the emissions. When tested under lab conditions the losses associated

with these IC engines were drastically reduced.



REFERENCES

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Ignition System for Improved Gasoline Engine Efficiency," SAE Technical Paper

2010-01-2110, 2010, doi: 10.4271/2010-01-2110

[3] Panchasara, H. V., 2010. “Spray Characteristics and Combustion Performance of

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Alabama.

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Development and Validation in the Context of a Pressure Chamber," SAE Technical Paper

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