Burned Fraction Research Articles

An Experimental and Modeling-Based Study Into the Ignition Delay Characteristics of Diesel Surrogate Binary Blend Fuels

This study examines the combustion characteristics of a binary mixture surrogate for possible future diesel fuels using both a single-cylinder research engine and a homogeneous reactor model using detailed chemical reaction kinetics. Binary mixtures of a normal straight-chain alkane (pure n-hexadecane, also known as n-cetane, C16H34) and an alkyl aromatic (toluene, C7H8) were tested in a single-cylinder research engine. Pure n-hexadecane was tested as a baseline reference, followed by 50%, 70%, and 80% toluene in hexadecane blends. Testing was conducted at fixed engine speed and constant indicated load. As references, two conventional petroleum-based fuels (commercial diesel and U.S. Navy JP-5 jet fuel) and five synthetic Fischer-Tropsch-based fuels were also tested. The ignition delay of the binary mixture surrogate increased with increasing toluene fraction and ranged from approximately 1.3 ms (pure hexadecane) to 3.0 ms (80% toluene in hexadecane). While ignition delay changed substantially, the location of 50% mass fraction burned did not change as significantly due to a simultaneous change in the premixed combustion fraction. Detailed chemical reaction rate modeling using a constant pressure, adiabatic, homogeneous reactor model predicts a chemical ignition delay with a similar trend to the experimental results but shorter overall magnitude. The difference between this predicted homogeneous chemical ignition delay and the experimentally observed ignition delay is defined as the physical ignition delay due to processes such as spray formation, entrainment, mixing, and vaporization. On a relative basis, the addition of 70% toluene to hexadecane causes a nearly identical relative increase in both physical and chemical ignition delay of approximately 50%. The chemical kinetic model predicts that, even though the addition of toluene delays the global onset of ignition, the initial production of reactive precursors such as HO2 and H2O2 may be faster with toluene due to the weakly bound methyl group. However, this initial production is insufficient to lead to wide-scale chain branching and ignition. The model predicts that the straight-chain alkane component (hexadecane) ignites first, causing the aromatic component to be consumed shortly thereafter. Greater ignition delay observed with the high toluene fraction blends is due to consumption of OH radicals by toluene. Overall, the detailed kinetic model captures the experimentally observed trends well and may be able to provide insight as to the relationship between bulk properties and physical ignition delay.

A study on fluidized bed combustion characteristics of corncob in three different combustion modes

This paper presents results obtained from corncob combustion in a pilot scale vortexing fluidized bed combustor (VFBC). Three combustion modes including direct combustion, staged combustion and flue gas recirculation (FGR) combustion were employed, and their combustion and pollutant emission characteristics were studied. In addition, the effects of combustion fraction and bed temperature on pollutant emission characteristics were investigated. The experimental results show that the combustion fractions vary with different combustion modes, resulting in different CO and NO emission characteristics. Staged and FGR combustions can reduce the NO emission concentration. Under similar working condition, NO concentration decreases by 30% in FGR mode, while 15% in staged mode compared with direct mode.

Burning Velocity of Propane–Air Mixtures from Pressure–Time Records during Explosions in a Closed Spherical Vessel

The flame propagation during the deflagration of the propane–air mixtures with variable initial concentration, pressure, and temperature ([C3H8] = 2.60–6.20 vol %, p0 = 30–200 kPa, and T0 = 298–433 K) in a spherical closed vessel with central ignition was monitored by means of pressure measurements. Using an improved relationship for the burnt mass fraction, the burning velocities were calculated from pressure–time records over an extended duration of spherical propagation. A very good agreement was found between the burning velocities of atmospheric laminar C3H8/air flames and literature data. Computed burning velocities, obtained from numerical modeling of one-dimensional laminar flames using two detailed chemical kinetic schemes (Warnatz mechanism and GRI Mech 3.0, respectively) are discussed in comparison to experimental burning velocities. The measured burning velocities are correlated with pressure and temperature using a power law; the baric and thermal exponents, ν and μ, lie within the usual range characteristic to alkane–air laminar flames.

Closed vessel combustion modelling by using pressure-time evolution function derived from two-zonal approach

In this paper a new method for burned mass fraction - pressure relation, x-p relation, for two-zone model combustion calculation is developed. The main application of the two-zone model is obtaining laminar burning velocity, SL, by using a pressure history from a closed vessel combustion experiment. The linear x-p relation by Lewis and Von Elbe is still widely used. For linear x-p relation, the end pressure is necessary as input data for the description of the combustion process. In this paper a new x-p relation is presented on the basis of mass and energy conservation during the combustion. In order to correctly represent pressure evolution, the model proposed in this paper needs several input parameters. They were obtained from different sources, like the PREMIX software (with GRIMECH 3.0 mechanism) and GASEQ software, as well as thermodynamic tables. The error analysis is presented in regard to the input parameters. The proposed model is validated against the experiment by Dahoe and Goey, and compared with linear x-p relation from Lewis and Von Elbe. The proposed two zone model shows sufficient accuracy when describing the combustion process in a closed vessel without knowing the end pressure in advance, i.e. both peak pressure and combustion rates can be sufficiently correctly captured.

Co-Firing Coal: Poultry Litter Biomass Blends in a Laboratory-Scale Boiler-Burner

Broiler chicken houses are an example of concentrated animal feeding operations that produce large amounts of animal waste that must be used or disposed of in an environmentally acceptable manner. Most of the collected poultry litter is used as fertilizer with or without intermediate storage (i.e., stockpiled). There are limits to the amount of manure that can safely be applied as fertilizer, and stored manure carries the risk of ground or surface water pollution. Combustion is proposed as an alternative method to safely dispose of excess poultry litter. The proposed disposal technique is mixing coal with poultry litter (e.g., 90:10 blend of coal:poultry litter by mass) and firing the resulting blended fuel in a convention utility boiler. This process is known as co-firing. The high temperatures produced by the coal allow the poultry litter to be completely combusted. Relative to coal, poultry litter biomass (LB) has a small heat value, high ash content, high sulfur content, and high nitrogen. All of these facts could lead to combustion and emissions problems when co-firing coal with litter biomass. In this research, the performance of a laboratory-scale boiler burner was evaluated while firing coal or coal:LB blends to determine the combustion performance. The carbon monoxide (CO) emissions for the fuels were similar, with the amount of CO produced being greater at lower excess air percentages. The burnt fraction for both of the fuels was between 0.80 and 0.95, showing that the addition of LB-based fuels does not adversely affect particle burnout. The pollutant emissions for the fuels were also evaluated, and the results show that the addition of litter biomass does not increase the emission of nitrous oxide (NO), even though the fuel nitrogen in the blended fuel is increased by 8% to 20% with the addition of 10% LB. The sulfur dioxide (SO2) emissions were also measured, but the results were inconclusive due to uncontrolled absorption of SO2 by the walls of the furnace. Overall, the results showed that switching from coal to a coal:LB blend does not result in a large decrease in boiler performance nor an increase in NO emissions, despite the relatively small reduction in fuel quality attributable to coal:LB blends.

Effects of hydraulic nozzle flow rate and high injection pressure on mixture formation, combustion and emissions on a single-cylinder DI light-duty diesel engine

Injection pressure and hydraulic nozzle flow rate are significant parameters that influence mixture formation and combustion in the direct injection (DI) diesel combustion process. An injection pressure increase enhances mixture formation as well as combustion. Decreasing the hydraulic flow rate, by means of reducing spray hole orifice diameter, affects mixture formation primarily through improved gas entrainment processes. Both injection pressure increase and hydraulic flow rate decrease therefore benefit mixture formation and combustion, which cause less soot emissions. Thus, the application of higher exhaust gas recirculation rates to decrease nitrogen oxide emissions is possible. The objective of this paper is to determine the effects of hydraulic flow rate variation in combination with very high injection pressures. Engine tests are carried out using a single-cylinder research engine, which is based on a light-duty DI diesel engine. With a displacement of 755 cm3 per cylinder, the engines range between typical passenger car (≈ 500 cm3) and medium-sized heavy-duty (≈ 1000 cm3) engines. The engine is equipped with a prototype common rail fuel injection system that is capable of delivering system pressures larger than 250 MPa. Four different hydraulic nozzle layouts are tested. The effects are presented for one part load and one full load operating condition. For each engine operating point, exhaust gas recirculation variations with different injection pressure levels and boost conditions are conducted. Evaluation of engine test results is performed at a constant soot/nitrogen oxide emission ratio of 1:10, which is relevant in engine calibration. Hydraulic measurements and the application of an empirical spray model support the interpretation of the engine test results. It is observed that a reduced hydraulic flow rate is beneficial for part load emission performance. It was found that a lower hydraulic flow rate causes a higher mean relative air/fuel ratio within the fuel spray and thus induces less soot formation. Moreover, the premixed fraction of combustion is enhanced through both injection pressure and hydraulic flow rate increases. In full load operation, the beneficial effect of reduced flow rates by means of smaller nozzle orifices cannot be detected. Parameters such as injection duration, combustion duration and spray momentum during spray/wall interaction are identified as more important. Boost pressure variation has only a minor effect on part load, whereas full load results are greatly influenced. In part load and full load operation, a limitation of the potential to reduce emissions is not observed within the investigated injection pressure range.

Effect of Swirl and Injection Pressure on Performance and Emissions of JP-8 Fueled High Speed Single Cylinder Diesel Engine

JP-8 is being closely watched as a suitable fuel for the “One fuel policy” by US Army. Some of the main targets of Army in the battle are the fuel economy and smoke/soot emissions. Soot emissions can be reduced in two ways, by increasing the injection pressure or by increasing swirl. An investigation was conducted to find out the more effective way to reduce soot emissions and to evaluate the influence of the swirl motion on JP-8 fuel combustion, performance and emissions in a single cylinder diesel engine. Increasing swirl increased heat losses and produced lower temperatures during injection process. Increasing swirl improved the premixed combustion fraction and produced higher peak temperatures and in turn increased NOx emissions. Increasing swirl also increased the nano-particle emissions.

Effect of Biodiesel, Jet Propellant (JP-8) and Ultra Low Sulfur Diesel Fuel on Auto-Ignition, Combustion, Performance and Emissions in a Single Cylinder Diesel Engine

Concern about the depletion of petroleum reserves, rising prices of conventional fuels, security of supply and global warming have driven research toward the development of renewable fuels for use in diesel engines. These fuels have different physical and chemical properties that affect the diesel combustion process. This paper compares between the autoignition, combustion, performance and emissions of soy-bean derived biodiesel, Jet propellant (JP-8) and ultra low sulfur diesel (ULSD) in a high speed single-cylinder research diesel engine equipped with a common rail injection system. Tests were conducted at steady state conditions at different injection pressures ranging from 600 bar to 1200 bar. The ‘rate of heat release’ traces are analyzed to determine the effect of fuel properties on the ignition delay, premixed combustion fraction and mixing and diffusion controlled combustion fractions. Biodiesel produced the largest diffusion controlled combustion fraction at all injection pressures compared to ULSD and JP-8. At 600 bar injection pressure, the diffusion controlled combustion fraction for biodiesel was 53% whereas both JP-8 and ULSD produced 39%. In addition, the effect of fuel properties on engine performance, fuel economy, and engine-out emissions is determined. On an average JP-8 produced 3% higher thermal efficiency than ULSD. Special attention is given to the oxides of nitrogen (NOx) emissions and particulate matter characteristics. On an average biodiesel produced 37% less NOx emissions compared to ULSD and JP-8.

Combustion instabilities and nanoparticles emission fluctuations in GDI spark ignition engine

The main challenge facing the concept of gasoline direct injection is the unfavourable physical conditions at which the premixed charge is prepared and burned. These conditions include the short time available for gasoline to be sprayed, evaporated, and homogeneously mixed with air. These conditions most probably affect the combustion process and the cycle-by-cycle variation and may be reflected in overall engine operation. The aim of this research is to analyze the combustion characteristics and cycle-by-cycle variation including engine-out nanoparticulates of a turbocharged, gasoline direct injected spark ignition (DISI) engine at a wide range of operating conditions. Gasoline DISI, turbo-intercooled, 1.6L, 4 cylinder engine has been used in the study. In-cylinder pressure has been measured using spark plug mounted piezoelectric transducer along with a PC based data acquisition. A single zone heat release model has been used to analyze the in-cylinder pressure data. The analysis of the combustion characteristics includes the flame development (0–10% burned mass fraction) and rapid burn (10–90% burned mass fraction) durations at different engine conditions. The cycle-by-cycle variations have been characterized by the coefficient of variations (COV) in the peak cylinder pressure, the indicated mean effective pressure (IMEP), burn durations, and particle number density. The combustion characteristics and cyclic variability of the DISI engine are compared with data from throttle body injected (TBI) engine and conclusions are developed.

The Impact of Saturated and Unsaturated Fuel Molecules on Diesel Combustion and Exhaust Emissions

Diesel fuels usually comprise a wide range of compounds having different molecular structures which can affect both the fuel's physical properties and combustion characteristics. In future, as synthetic fuels from fossil and sustainable sources become increasingly available, it could be possible to control the fuel's molecular structure to achieve clean and efficient combustion. This paper presents experimental results of combustion and emissions studies undertaken on a single cylinder diesel engine supplied with 18 different fuels each comprising a single, acyclic, non-oxygenated hydrocarbon molecule. These molecules were chosen to highlight the effect of straight carbon chain length, degree of saturation and the addition of methyl groups as branches to a straight carbon chain. The engine tests were carried out at constant injection timing and they were repeated at constant ignition timing and at constant ignition delay, the latter being achieved through the addition to the various fuels of small quantities of ignition improver (2-ethylhexyl nitrate). In tests conducted at constant injection and constant ignition timing the ignition delay of the molecule was found to be the primary driver of combustion phasing, the balance between premixed and diffusion-controlled combustion and, thereby, exhaust emissions. However, the elimination of ignition delay as a variable, using ignition improver, revealed further, subtler, secondary combustion effects also attributable to the molecular structure of the fuels tested. For example, with constant ignition delay, the premixed burn fraction and oxides of nitrogen in the exhaust for the various fuels correlated well with the volatility and the adiabatic flame temperature.

On Comparative Performance Testing of Prechamber and Open Chamber Laser Ignition

Laser ignition is a potential ignition technology to achieve reliable lean burn ignition in high brake mean effective pressure (BMEP) internal combustion engines. The technology has the potential to increase brake thermal efficiency and reduce exhaust emissions. This submission reports on engine testing of a Caterpillar G3516C stationary natural gas fueled engine with three types of ignition approaches: (i) nonfueled electric prechamber plug with electrodes at the base of the prechamber, (ii) nonfueled laser prechamber plug with laser spark in the middle of the prechamber, and (iii) open chamber plug with laser spark in the main chamber. In the second configuration, a stock nonfueled prechamber plug was modified to incorporate a sapphire window and a focusing lens to form a laser prechamber plug. A 1064 nm Q-switched Nd:YAG laser was used to create laser sparks. For these tests, a single cylinder of the engine was retrofitted with the laser plug while the remaining cylinders were run with conventional electric ignition system at baseline ignition timing of 24 deg before top dead center (BTDC). The performances of the three plugs were compared in terms of indicated mean effective pressures (IMEP), mass burn fraction duration and coefficient of variation (COV) of IMEP, and COV of peak pressure location. Test data show comparable performance between electric and laser prechamber plugs, albeit with a lower degree of variability in engine’s performance for electric prechamber plug compared to the laser prechamber plug. The open chamber plug exhibited poorer variability in engine performance. All results are discussed in the context of prechamber and engine fluid mechanics.

Statistical analysis of the cyclic variations of heat release parameters in HCCI combustion of methanol and gasoline

Combustion instability and cyclic variations lead to the requirement of closed loop control for use of homogeneous charge compression ignition (HCCI) engine technology for automotive applications. The closed loop control of HCCI combustion requires robust combustion timing parameters with a systematic and detailed study of its variations vis-à-vis engine operating conditions. An experimental study is conducted to provide insight into cyclic variations of HCCI combustion phasing for two fuels (gasoline and methanol) using statistical techniques. In this study, cycle-to-cycle variations of heat release parameters such as Maximum Rate of Heat Release (ROHRmax), 10% Mass Burn Fraction (MBF), 50% MBF, 90% MBF and Indicated Mean Effective Pressure (IMEP) of HCCI combustion engine fueled with methanol and gasoline were investigated using a modified two-cylinder, four-stroke engine. The experiments were conducted with different engine operating conditions at constant intake air temperature (140°C) and different air–fuel ratios at constant engine speed (1500rpm). To evaluate the cycle-to-cycle variations of combustion parameters at different test conditions, coefficient of variation (COV) and standard deviation of parameters were used. The results showed that CA50 (crank angle position of 50% MBF) is a robust parameter for the closed loop control of HCCI combustion.

Investigation of the effects of hydrogen on cylinder pressure in a split-injection diesel engine at heavy EGR

The distinctive properties of hydrogen have initiated considerable applied research related to the internal combustion engine. Recently, it has been reported that NO x emissions were reduced by using hydrogen in a diesel engine at low temperature and heavy EGR conditions. As the continuing study, cylinder pressure was also investigated to determine the combustion characteristics and their relationship to NO x emissions. The test engine was operated at constant speed and fixed diesel fuel injection rate (1500 rpm, 2.5 kg/h). Diesel fuel was injected in a split pattern into a 2-L diesel engine. The cylinder pressure was measured for different hydrogen flow rates and EGR ratios. The intake manifold temperature was controlled to be the same to avoid the gas intake temperature variations under the widely differing levels (2%–31%) of EGR. The measured cylinder pressure was analyzed for characteristic combustion values, such as mass burn fraction and combustion duration. The rising crank angle of the heat release rate was unaffected by the presence of hydrogen. However, supplying hydrogen extended the main combustion duration. This longer main combustion duration was particularly noticeable at the heavy EGR condition. It correlated well with the reduced NO x emissions.

Estimation of double-Wiebe function parameters using least square method for burn durations of ethanol-gasoline blends in spark ignition engine over variable compression ratios and EGR levels

Abstract Phasing and duration are two of the most important aspects of combustion in Spark Ignition (SI) engines. They impact efficiency, emissions, and overall engine performance. These aspects of combustion can be represented by the mass fraction burn (MFB) profile. Having an accurate mathematical model of the MFB profile leads to an ability to model the combustion process and, thus, properly model the overall engine in 1D engine simulation tools. The Wiebe function is widely used in engine simulation to estimate the MFB profile as a function of crankshaft position. In this work, for the purpose of validating a sub-process, the Wiebe function parameters were calculated using an analytical solution and a least squares method by fitting MFB locations, as determined from analysis of measured cylinder pressure, to both single and double-Wiebe functions. To determine the accuracy of the respective Wiebe function, a single-zone pressure model was applied to reconstruct the pressure trace. Once the pressure trace is recovered, the reconstructed pressure trace is then compared with the experimentally measured cylinder pressure trace. Results showed that the double-Wiebe function model fit better than the single-Wiebe function model. The root mean square error (RMSE) of the reconstructed pressure trace using the double-Wiebe estimation is 7.9 kPa. In comparison, the RMSEs of the reconstructed pressure traces using the single-Wiebe analytical solution and single-Wiebe least squares methods were 70.0 kPa and 75.9 kPa, respectively, demonstrating a significant improvement.

Performance, emission and combustion characteristics of a variable compression ratio engine using methyl esters of waste cooking oil and diesel blends

The performance, emission and combustion characteristics of a single cylinder four stroke variable compression ratio multi fuel engine when fueled with waste cooking oil methyl ester and its 20%, 40%, 60% and 80% blends with diesel (on a volume basis) are investigated and compared with standard diesel. The suitability of waste cooking oil methyl ester as a biofuel has been established in this study. Bio diesel produced from waste sun flower oil by transesterification process has been used in this study. Experiment has been conducted at a fixed engine speed of 1500 rpm, 50% load and at compression ratios of 18:1, 19:1, 20:1, 21:1 and 22:1. The impact of compression ratio on fuel consumption, combustion pressures and exhaust gas emissions has been investigated and presented. Optimum compression ratio which gives best performance has been identified. The results indicate longer ignition delay, maximum rate of pressure rise, lower heat release rate and higher mass fraction burnt at higher compression ratio for waste cooking oil methyl ester when compared to that of diesel. The brake thermal efficiency at 50% load for waste cooking oil methyl ester blends and diesel has been calculated and the blend B40 is found to give maximum thermal efficiency. The blends when used as fuel results in reduction of carbon monoxide, hydrocarbon and increase in nitrogen oxides emissions.

정적연소기에서 토치의 체적 변화에 따른 메탄의 연소특성 파악

Six different size of torch-ignition device were applied in a constant volume combustion chamber for evaluating the effects of torch-ignition on combustion. The torch-ignition device was designed for six different volumes and same orifice size. The combustion pressures were measured to calculate the mass burn fraction and combustion enhancement rate. In addition, the flame propagations were visualized by shadowgraph method for the qualitative comparison. The result showed that the combustion pressure and mass burn fraction were increased when using the torch ignition device. And the combustion duration were decreased. The combustion enhancement rates of torch-ignition cases were improved in comparison with conventional spark ignition. Finally, the visualization results showed that the torch-ignition induced faster burn than conventional spark ignition due to the earlier transition to turbulent flame and larger flame surface, during the initial stage. Finally, the initial flame propagation was affected by torch-ignition volume.

Forest management strategies for dealing with fire-related uncertainty when managing two forest seral stages

Ecological values are an important aspect of sustainable forest management, but little attention has been paid to maintaining these values when using traditional linear programming (LP) forest management planning models in uncertain planning environments. We embedded an LP planning model that specifies when and how much to harvest in a simulation model of a “managed” flammable forest landscape. The simulation model was used to evaluate two strategies for dealing with fire-related uncertainty when managing mature and old forest areas. The two seral stage areas were constrained in the LP planning model to a minimum of 10% of the total forest area and the strategies were evaluated under four representative fire regimes. We also developed a risk analysis tool that can be used by forest managers that wish to incorporate fire-related uncertainty in their decision-making. We found that use of the LP model would reduce the areas of the mature and old forest to their lower bound and fire would further reduce the seral areas below those levels, particularly when the mean annual burn fraction exceeds 0.45% per annum. Increasing the minimum area required (i.e., the right-hand side of the constraint) would increase the likelihood of satisfying the minimum area requirements.

Estimation of Combustion Phasing Using the Combustion Net Torque Method

AbstractA new and computationally efficient method, called the combustion net torque method, for estimating combustion phasing in an internal combustion engine using crankshaft torque data is presented. The work is motivated by the need of such an estimation method for real-time implementation of a torque based closed-loop combustion phasing control system. The ideal properties of the proposed method, based on torque calculated from cylinder pressure, are studied using simulations and experimental data from both a spark ignited and a compression ignited engine. A relation to 50% burned mass fraction, the most common measure of combustion phasing, is established and the robustness of the method is investigated. The results show that the ideal estimation accuracy of the proposed method is high, especially around the combustion phasing position where maximum engine efficiency is achieved. Also, the computational complexity of the combustion net torque method is significantly lower compared to other existing techniques for torque domain combustion phasing estimation.

Combustion Characteristics of Methane in A Direct Injection Engine Using Spark Plug Fuel Injector

The combustion characteristics of methane in a direct injection spark ignition engine using Spark Plug Fuel Injector (SPFI) was investigated. SPFI is a system developed to convert any externally-mixing (port injection, carburetor) spark ignition engine to direct injection by combining fuel injectors into spark plugs. The burning rates of methane were measured using normalized combustion pressure method, where the normalized pressure rise due to combustion is equivalent to the mass fraction burnt at the specific crank angle. A single cylinder research engine was installed with the SPFI system. Cylinder pressures were taken with engine running at 1100 rpm and stoichiometric air/fuel ratio. The spark timing was set at 25 o BTDC. For comparison, the engine was run with methane port injection. The optimal fuel injection timing with SPFI was found to be 170 o BTDC. Results showed that SPFI direct injection, increased the volumetric efficiency by 11% compared to port injection, resulting in higher heating value of cylinder charge per cycle. Combustion analysis show that the overall burning rate of methane direct injection is faster than the ones of port injection although is slower at the initial stage. Injection pressures affect ignition delay but not the combustion duration. Changing mixture stoichiometry affects the magnitude of ignition delay. Combustion duration increases with leaner mixture. Different load conditions have significant effect on combustion process. Lower loads tend to increase combustion duration but shorten ignition delay. SPFI Di methane system has the potential of increasing engine performance due to increased volumetric efficiency and faster burning rate.

An indirect-drive non-cryogenic double-shell path to 1ω Nd-laser hybrid inertial fusion–fission energy

A high-yield, room temperature, double-shell target design using a Nd : glass laser driver at the fundamental frequency 1ω is developed for hybrid inertial fusion–fission energy generation (Moses et al 2009 Fusion Sci. Technol. 56 547). The associated 4–10× fission energy gain relaxes the gain requirements of the fusion driver, enabling the prospect of a volume-ignition target with high thermonuclear burn fraction, simplified (1ω) laser operations from a quasi-impulsive power history, room temperature fielding, minimal shock-timing requirements and reduced risk of plasma-mediated laser backscatter with a vacuum hohlraum.