Thermodynamic properties of hydrocarbon/air plasma mixtures at ultra-high temperatures must be precisely calculated due to important influence on the flame kernel formation and propagation in combusting flows and spark discharge applications. A new algorithm based on the complete chemical equilibrium assumption is developed to calculate the ultra-high temperature plasma composition and thermodynamic properties, including enthalpy, entropy, Gibbs free energy, specific heat at constant pressure, specific heat ratio, speed of sound, mean molar mass, and degree of ionization. The method is applied to compute the thermodynamic properties of H2/air and CH4/air plasma mixtures for different temperatures (1000–100 000 K), different pressures (10-6–100 atm), and different fuel/air equivalence ratios within flammability limit. In calculating the individual thermodynamic properties of the atomic species needed to compute the complete equilibrium composition, the Debye-Huckel cutoff criterion has been used for terminating the series expression of the electronic partition function so as to capture the reduction of the ionization potential due to pressure and the intense connection between the electronic partition function and the thermodynamic properties of the atomic species and the number of energy levels taken into account. Partition functions have been calculated using tabulated data for available atomic energy levels. The Rydberg and Ritz extrapolation and interpolation laws have been used for energy levels which are not observed. The calculated plasma properties are then presented as functions of temperature, pressure and equivalence ratio, in terms of a new set of thermodynamically self-consistent correlations that are shown to provide very accurate fits suitable for efficient use in CFD simulations. Comparisons with existing data for air plasma show excellent agreement.

Pumping losses are one of the primary energy losses in throttled spark ignition engines. In order to reduce fuel consumption, engine manufacturers are incorporating devices that deactivate the valve-train in some cylinders. In the operating strategies currently implemented in the market, fixed sets of cylinders are deactivated, allowing 2 or 3 operating modes. In contrast, Tula Technology has developed Dynamic Skip Fire (DSF), in which the decision of whether or not to fire a cylinder is decided on a cycle-by-cycle basis. Testing the DSF technology in an independent certified lab on a 2010 GMC Denali, reduces the fuel consumption by 18% on a cycle-average basis, and simultaneously increases the ability to mitigate noise and vibration at objectionable frequencies. This paper outlines the results of the experiments that have been conducted on an eight cylinder engine over a wide range of conditions to investigate the fuel consumption gains and emissions impact when incorporating DSF technology. The experiments have been carried out over a wide range of engine speeds, loads, and DSF strategies and significant improvements have been observed. Introduction Pumping losses are one of the major sources of thermal efficiency losses in spark ignition engines. Cylinder deactivation reduces the pumping losses by deactivating cylinders during every engine cycle based on torque requirements. As a means to improve engine efficiency, cylinder deactivation has a long history. It has been employed by General Motors’s Active Fuel Management (AFM) system in eight cylinder engines [1]. In their approach, four of eight cylinders are deactivated in a 5.3L or 6.2L OHV V8 engine; meaning that a fixed pattern of deactivation is applied and fully implemented in each engine cycle. Other OEMs have also used cylinder deactivation [2-3]. For instance in VW’s 1.4-liter TSI 4cylinder engine, cylinders 2 and 3 are deactivated [2]. Similar to [1], in VW’s engine a fixed pattern of deactivation is implemented and completed in each engine cycle. In this firing pattern, a deactivated cylinder is always followed by a firing cylinder event in each engine cycle. Although firing every other cylinder is the most common approach, some deactivation strategies have used other approaches. For instance, Honda has fired two out of every three cylinders in a 3.5L i-VTEC engine [3]. At Tula Technology, we have introduced Dynamic Skip Fire (DSF) an evolved version of deactivation which is capable of deactivating the cylinders without any limitation. DSF deactivates cylinders in a manner that achieves the load demanded while avoiding objectionable noise and vibration. For example, Figure 1 displays a DSF pattern of 1 fire followed by 2 skips for each cylinder. Figure 1 shows that three cycles are required to achieve this pattern. Figure 1: DSF operation of 1 fire 2 skips for each cylinder in an eight cylinder engine Along with rewarding achievements of DSF, there are also some challenges. Choosing the firing density based only upon fuel economy would induce undesirable NVH characteristics. Each fire induces a torque which creates an acceleration exerted to the crankshaft. The acceleration causes vibrations whose frequency is a function of firing density and firing pattern. Due to the variable nature of DSF in terms of firing frequency, great care should be taken to avoid frequencies in which perception of vibration or resonance is encountered. More details about evaluation and mitigation of NVH in Tula DSF can be found in [5]. One of the benefits of DSF is the wide range of firing pattern selections to minimize the resonance modes. This capability of DSF provides us the opportunity to choose firing patterns which produce surprisingly lower NVH than V8 at equivalent power. Besides NVH considerations, our FTP cycle data for L94 engine (employed in 2010 GMC Denali) show fuel economies of 19.92 mpg at DSF versus 17.34 mpg at V8 mode. Meaning, DSF reduces fuel consumption by 14-18% over V8 [6]. In Tula’s previous publications (e.g. [5, 6]), the fundamental concepts of DSF, have been discussed. In this paper we are presenting a comparative study of DSF advantages versus V8 mode. We will discuss the results in a wide range of operational conditions (listed in

Achieving effective ignition of reacting mixtures using nanosecond pulsed discharge non-equilibrium transient plasma (TP), requires that the effects of several experimental parameters be quantified and understood. Among them are the electrode geometry, the discharge location especially in non-premixed systems, and the relative ignition performance by spark and TP under the same experimental conditions. In the present investigation, such issues were addressed experimentally using a cylindrical constant volume combustion chamber and a counterflow flame configuration coupled with optical shadowgraph that enables observation of how and where the ignition process starts. Results were obtained under atmospheric pressure and showed that the electrode geometry has a notable influence on ignition, with the needle-to-semicircle exhibiting the best ignition performance. Furthermore, it was determined that under non-premixed conditions discharging TP in the reactants mixing layer was most effective in achieving ignition. It was also determined that in the cases considered, the TP induced ignition initiates from the needle head where the electric field and electron densities are the highest. In the case of a spark, however, ignition was found to initiate always from the hot region between the two electrodes. Comparison of spark and TP discharges in only air (i.e. without fuel) and ignition phenomena induced by them also suggest that in the case of TP ignition is at least partly non-thermal and instead driven by the production of active species. Finally, it was determined that single pulsed TP discharges are sufficient to ignite both premixed and non-premixed flames of a variety of fuels ranging from hydrogen to heavy fuels including F-76 diesel and IFO380 bunker fuel even at room temperature.

In this paper, the laminar burning speed of Jet Fuel (Jet-A) and three different samples of JP-8 are investigated. The autoignition properties of JP-8 fuels are also explored. These experiments have been done in a spherical vessel at high temperatures and pressures with different equivalence ratios. The pressure data were recorded by a Kistler pressure transducer, and intense fluctuations of pressure data were observed during the explosion of the unburned gas zone. It is observed that Jet Fuel and JP-8/air mixtures have very similar burning speed. Also, autoignition of these fuels is very sensitive to a specific range of temperature rather than pressure.

The laminar burning speeds of Jet-A/air and three different samples of jet propellant (JP-8)/air mixtures have been measured and the onset of auto-ignition in JP-8/air premixed mixtures has been determined. The experiments were made in a constant volume spherical vessel, which can withstand high pressures up to 400 atm. Burning speed was calculated from dynamic pressure rise due to the combustion process in the vessel. A thermodynamic model based on the pressure rise was used to determine the burning speed. The burning speeds were measured in lean mixtures for pressures of 1–4.5 atm and temperatures of 493–700 K. The onset of auto-ignition of JP-8 fuels was evaluated by observing intense fluctuations of pressure data during the explosion of the unburned gas. It was revealed that Jet-A and JP-8 have very similar burning speeds; however, auto-ignition temperatures of various samples of JP-8 were slightly different from each other. Auto-ignition of these fuels was much more sensitive to temperature rather than pressure.

Experimental studies have been performed to investigate the flame structure and laminar burning speed of JP-8/oxidizer/diluent premixed flames at high temperatures and pressures. Three different diluents including argon, helium, and a mixture of 14% CO2 and 86% N2 (extra diluent gases), were used. The experiments were carried out in two constant volume spherical and cylindrical vessels. Laminar burning speeds were measured using a thermodynamics model based on the pressure rise method. Temperatures from 493 to 700K and pressures from 1 to 11.5atm were investigated. Extra diluent gases (EDG) decrease the laminar burning speeds but do not greatly impact the stability of the flame compared to JP-8/air. Replacing nitrogen in the air with argon and helium increases the range of temperature and pressure in the experiments. Helium as a diluent also increases the temperature and pressure range of stable flame as well as the laminar burning speed. Power law correlations have been developed for laminar burning speeds of JP-8/air/EDG and JP-8/oxygen/helium mixtures at a temperature range of 493–700K and a pressure range of 1–10atm for lean mixtures.

Laminar burning speed of ethanol/air/diluent mixtures have been measured over a wide range of temperature, pressure, fuel air equivalence ratio and diluent. Experimental facilities include a cylindrical vessel with two large end windows and a spherical vessel with capability to withstand pressures up to 425atm. Both of these vessels are heated for having initial temperatures of unburned gas up to 500K. A shadowgraph system with a CMOS camera capable of taking pictures up to 40,000frames/s is used to observe structure of propagating flames. Pressure rise due to combustion in both vessels is used to calculate laminar burning speed of the mixture. A thermodynamic model is used to calculate burning speed from combustion pressure. Laminar burning speeds of ethanol/air premixed mixtures have been measured at high temperatures and pressures. A mixture of 86% nitrogen and 14% carbon dioxide, which simulate heat capacity of residual gases in internal combustion engines, is used to determine the effect of diluent on burning speed. A correlation for laminar burning speed as a function of temperature, pressure, equivalence ratio and extra diluent gas (EDG) has been developed. The range of temperature and pressure are 300–650K and 1–5atm, fuel air equivalence ratio 0.8–1.1 and extra diluent gases of 5% and 10%. The measured values compare very well with available data and extend the range many folds.

Thermodynamic properties of ionized gases at high temperatures have been calculated by a new model based on local equilibrium conditions. Calculations have been done for nitrogen, oxygen, air, argon, and helium. The temperature range is 300–100,000 K. Thermodynamic properties include specific heat capacity, density, mole fraction of particles, and enthalpy. The model has been developed using statistical thermodynamics methods. Results have been compared with other researchers and the agreement is good.

Fundamental concepts of laminar flames have been studied both experimentally and theoretically. Topics such as, thermodynamic properties of gases at high temperatures, plasma formation in argon and air, flame kernel development, flame structure, burning speed of jet fuels such as ethanol, JP-8 and biomass based fuel have been studied.

Plasma kernel formation of argon is studied experimentally and theoretically. The experiments have been performed in a constant volume cylindrical vessel located in a shadowgraph system. The experiments have been done at constant pressure. The energy of plasma is supplied by an ignition system using two electrodes located in the vessel. The experiments have been done with two different spark energies to study the effect of input energy on kernel growth and its properties. A thermodynamic model employing mass and energy balances was developed to predict the experimental data. The agreement between the experiments and model prediction is very good. The effect of various parameters such as initial temperature, initial radius of the kernel, and the radiation loss have been investigated and it has been concluded that the initial condition is very important on the formation and expansion of the kernel.

Flame kernel formation and propagation in premixed gases have been studied experimentally and theoretically. The experiments have been carried out at constant pressure and temperature in a constant volume vessel located in a high speed shadowgraph system. The formation and propagation of the hot plasma kernel has been simulated for inert gas mixtures using a thermodynamic model. The effects of various parameters including the discharge energy, radiation losses, initial temperature and initial volume of the plasma have been studied in detail. The experiments have been extended to flame kernel formation and propagation of methane/air mixtures. The effect of energy terms including spark energy, chemical energy and energy losses on flame kernel formation and propagation have been investigated. The inputs for this model are the initial conditions of the mixture and experimental data for flame radii. It is concluded that these are the most important parameters effecting plasma kernel growth. The results of laminar burning speeds have been compared with previously published results and are in good agreement.

A thermodynamic model has been developed to calculate burning speed and entropy production of transient expending spherical laminar flame in an enclosed vessel. The model also predicts the particle trajectories of both unburned and burned gases in the vessel. The input to this model is the dynamic pressure rise due to combustion process. The unburned gases are divided into three regions: The core unburned gases which are compressed isentropically, the vessel walls and electrodes boundary layer gases, and gases in the preheat zone of the flames. The burned gases are in many shells having the same pressure but different temperatures. The model also includes radiation losses from the burned gases to vessel walls. Entropy production due to irreversibility has been calculated by applying entropy balance to the gas mixtures. Burning speed of premixed n-decane air mixture has been reported for temperatures and pressures along an isentrope.

Jet propellant 8 (JP-8)/air laminar burning speed was experimentally measured and its flame structure was studied at high temperatures and pressures using a high-speed camera. The experimental facilities included a spherical vessel, used for the measurement of burning speed, and a cylindrical vessel, used in a shadowgraph system to study flame shape and structure and to measure burning speed. A thermodynamic model was developed to calculate burning speeds using the dynamic pressure rise in the vessel due to the combustion process. The model consists of a central burned gas core of variable temperature surrounded first by a reaction sheet, then by an unburned gas shell with uniform temperature and lastly by thermal boundary layers at the wall and electrodes. Radiation from burned gases to the walls was also included in the model. Burning speeds of laminar flames of JP-8/air were calculated for a wide range of conditions. A Power law correlation was developed to calculate laminar burning speed at temperatures ranging from 500–700K, pressures of 1–6atm and equivalence ratios of 0.8–1. Flame structure and cell formations were observed using an optical system. Experimental results showed that pressure and the fuel–air equivalence ratio have a strong influence on flame structure.

A thermodynamic model to calculate burning speed of methane-air-diluent mixtures from the measured dynamic pressure rise of a combustion process in a chamber has been developed. The effect of automotive exhaust gas on the burning speeds was measured using a mixture of 86 % N2 and 14 % CO2 as the diluent. Photographic observations were made through the end windows in the cylindrical chamber using a high-speed charged coupled device (CCD) camera with variable speed of up to 8000 frames/second. The measured values of burning speeds have been compared with laminar burning speeds calculated using the PREMIX flame speed code and the GRI-Mech 3.0 mechanism. This thermodynamic model is valid for a wide range of high temperatures and pressures and the results agree well with the measurements under these conditions when the flames are smooth or cracked and lean or stochiometric.

Flame kernel formation and structure is a fundamental factor of spark ignition engines’ performance. An experimental study about the effect of spark electrode geometry on premixed flame propagation has been done with methane-air premixed mixtures. The experimental system consists of a constant volume cylindrical vessel and a shadowgraph optical system. Experiments were performed at atmospheric initial pressure with various equivalence ratios and spark electrode geometries. Flame propagation pictures and movies were taken by a CMOS high speed camera at 10,000 frames per second. Flame radii were measured by MIDAS software and parameters affecting flame location and formation were investigated. Experimental results show that the spark electrode thickness and its tip impact flame location and structure propagation.

Autoignition and explosion limits of JP-8/air mixtures have been investigated by performing a set of experiments in a spherical vessel. These experiments have been done in high temperatures and pressures with different equivalence ratios. The pressure data were recorded by a Kistler pressure transducer, and intense fluctuations of pressure data were observed during the explosion of the unburned gas zone. Three ionization probes were screwed on the vessel to pinpoint the arrival of the flame to the wall and any kind of abnormal signal from these devices Could be a reason of autoignition in the end gas. There is a specific range of temperatures and pressures in which explosion Occurs. It was concluded that JP-8/air mixtures are very sensitive to a specific range of temperature rather than pressure.

The focus of this study is the calculation of the laminar burning speed of JP-8, oxygen, and helium mixtures at high temperatures and pressures. Two constant volume combustion vessels were used for the analysis. The spherical vessel was primarily used for the collection of pressure data from which the burning speed was calculated. A cylindrical vessel was also used in conjunction with a shadowgraph system to observe the flame structure and the onset of instability. Observations of JP-8 with both nitrogen and helium as diluents were made in the cylindrical vessel and it was seen that at a temperature of 200° C over the range of 1-8 atmospheres pressure and equivalence ratios of 0.7-1.0 with helium as the diluent, the flame was laminar throughout its combustion. Pressure measurements of JP-8 and oxygen with helium as the diluent were then made in the spherical vessel. Laminar burning speed of JP-8 with oxygen and helium has been calculated using the spherical vessel pressure data for this range of temperatures, pressures and equivalence ratios. Power law correlations for burning speeds have been developed for these results.