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

Seminar Report 2015-16
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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.

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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.

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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.

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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.

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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. .

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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

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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.

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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.

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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

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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
𝑃𝑃1 𝑉𝑉1
𝑇𝑇1
=
𝑃𝑃2 𝑉𝑉2
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 = � 𝑃𝑃𝑃𝑃𝑃𝑃 = (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.

20
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.

21
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 =
𝟓𝟓,𝟕𝟕𝟕𝟕𝟕𝟕,𝟑𝟑𝟑𝟑𝟑𝟑
(𝟖𝟖∗𝟓𝟓𝟓𝟓.𝟑𝟑)+(𝟗𝟗∗𝟑𝟑𝟑𝟑.𝟕𝟕)
= 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 ℃

22
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’

23
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.

24
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

25
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.

26
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.

27
REFERENCES
[1] 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” SAE
Technical Paper 2013-01-0257, 2013, doi:10.4271/2013-01-0257.
[2] De Boer, C., Chang, J., and Shetty, S., "Transonic Combustion - A Novel Injection-
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
Unheated and Preheated Liquid Biofuels,” Tuscaloosa, Alabama, USA: University of
Alabama.
[4] Hossain, K., Qiu, J., Shetty, S., Zoldak, P. et al., "Transonic Combustion: Model
Development and Validation in the Context of a Pressure Chamber," SAE Technical Paper
2012-01-0155, 2012, doi:10.4271/2012-01-0155.
[5] Zoldak, P., de Boer, C., and Shetty, S., "Transonic Combustion - Supercritical Gasoline
Combustion Operating Range Extension for Low Emissions and High Thermal
Efficiency," SAE Technical Paper 2012-01-0702, 2012, doi:10.4271/2012-01-0702.

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