Constant Volume Combustion Chamber Research Articles

An experimental and modeling study of ammonia with enriched oxygen content and ammonia/hydrogen laminar flame speed at elevated pressure and temperature

Laminar flame speeds of ammonia with oxygen-enriched air (oxygen content varying from 21 to 30 vol.%) and ammonia-hydrogen-air mixtures (fuel hydrogen content varying from 0 to 30 vol.%) at elevated pressure (1–10 bar) and temperature (298–473 K) were determined experimentally using a constant volume combustion chamber. Moreover, ammonia laminar flame speeds with helium as an inert were measured for the first time. Using these experimental data along with published ones, we have developed a newly compiled kinetic model for the prediction of the oxidation of ammonia and ammonia-hydrogen blends in freely propagating and burner stabilized premixed flames, as well as in shock tubes, rapid compression machines and a jet-stirred reactor. The reaction mechanism also considers the formation of nitrogen oxides, as well as the reduction of nitrogen oxides depending on the conditions of the surrounding gas phase. The experimental results from the present work and the literature are interpreted with the help of the kinetic model derived here. The experiments show that increasing the initial temperature, fuel hydrogen content, or oxidizer oxygen content causes the laminar flame speed to increase, while it decreases when increasing the initial pressure. The proposed kinetic model predicts the same trends than experiments and a good agreement is found with measurements for a wide range of conditions. The model suggests that under rich conditions the N2H2 formation path is favored compared to stoichiometric condition. The most important reactions under rich conditions are: NH2+NH=N2H2+H, NH2+NH2=N2H2+H2, N2H2+H=NNH+H2 and N2H2+M=NNH+H+M. These reactions were also found to be among the most sensitive reactions for predicting the laminar flame speed for all the cases investigated.

Spherically expanding flame in silane–hydrogen–nitrous oxide–argon mixtures

The effect of silane addition on the laminar flame speed (Su0) of flames propagating in hydrogen–nitrous oxide–argon mixtures has been investigated experimentally for the first time using the spherically expanding flame technique in a constant volume combustion chamber. Replacing hydrogen by silane and maintaining the equivalence ratio constant, much higher flame speeds, explosion peak pressures, and pressure rise coefficients were measured. A previously developed detailed reaction model has been updated based on ab initio thermodynamic properties calculations and collision limit violation analysis. The improved reaction model demonstrates encouraging performance in predicting the flame speed, with a mean absolute error below 11%. To explain the effect of silane addition on the flame dynamics, a number of parameters have been calculated including OH and H rate of production, heat release rate per reaction, and sensitivity coefficient on Su0. The dynamics of freely propagating flames in SiH4–H2–N2O–Ar mixtures is essentially controlled by reactions of the H–O–N chemical system: N2O+H=N2+OH, OH+H2=H2O+H, and N2O(+M)=N2+O(+M). Whereas silane addition does not influence much the rate of production of OH, it significantly modifies that of H with a number of pyrolytic chemical pathways of silicon hydrides, such as SiH+H2=SiH2+H and Si+H2=SiH+H, which act as sink of H atom as they proceed in the backward direction. The reactions forming SiO(s) and SiO2(s), such as SiO+OH=SiO2(s)+H and 2SiO=2SiO(s), are exothermic and significantly contribute to the temperature increase. The adiabatic, constant pressure flame temperature for mixture containing silane is significantly higher, up to several 100’s K. The increase of Su0 induced by silane addition seems to be mostly related to the large increase of the flame temperature which leads to higher energy release rate.

Experimental study on premixed turbulent flame of methane/air in a spherical closed chamber

A turbulent combustion test platform is designed. It is demonstrated that the turbulent environment in a constant volume combustion chamber is isotropic and controllable. Based on the platform, the turbulent combustion characteristics of methane/air are studied. The collected flame image and combustion pressure data are analysed. The results show that when the initial temperature is 300 K, the initial pressure is 1 bar, and the equivalence ratio is ϕ=1, the flame shape maintains self-similarity in the propagation process under different turbulence intensities. With the increase in turbulence intensity, there are more cracks on the flame surface and more wrinkles on the flame front; with the increase in turbulence intensity, the combustion propagation rate increases, the flame propagation rate increases at the same flame radius, and the maximum combustion pressure and the rate of pressure rise increase. When the turbulence intensity is constant, the test results of equivalence ratios of 0.8, 1.0 and 1.2 are compared. At an equivalent ratio of 1, the flame propagation rate and the stretch rate of the flame are maximized, and the maximum burning pressure and pressure rise rate are maximized.

Autoignition characteristics of bio-based fuels, farnesane and TPGME, in comparison with fuels of similar cetane rating

Bio-based alternative fuels have received increasing attention with growing concerns about depletion of fossil reserves and environmental deterioration. The development of new combustion concepts in internal combustion engines requires a better understanding of autoignition characteristics of the bio-based alternative fuels. This study investigates two cases of alternative fuels, namely, a kerosene-type fuel farnesane and an oxygenated fuel, TPGME, and compares those fuels with full-boiling range of fuels with similar cetane number. The homogeneous autoignition and spray ignition characteristics of the selected fuels are studied using a modified CFR octane rating engine and a cetane rating instrument, respectively. When comparing farnesane with a full-boiling range counterpart (HRJ8), their similar cetane ratings result in comparable combustion heat release, but the overall ignition reactivity of farnesane is stronger than HRJ8 during the pre-ignition process. Results from a constant volume spray combustion chamber indicate that the spray process of farnesane and HRJ8 strongly influences the overall ignition delay of each fuel. Despite the similar cetane ratings of TPGME and n-heptane, TPGME shows greater apparent low-temperature oxidation reactivity at low compression ratios in the range from CR 4.0-5.5 than n-heptane. A simplified model focused on the key reaction pathways of low-temperature oxidation of TPGME has been applied to account for the stronger low-temperature reactivity of TPGME, supported by density functional theory (DFT) calculations. Regardless of the similar cetane ratings of the fuels, n-heptane and JP-8/SPK lead to similar total ignition delay times, while TPGME shows the shortest overall ignition delay times in the constant volume combustion chamber.

Spray combustion and soot formation characteristics of the acetone-butanol-ethanol/diesel blends under diesel engine-relevant conditions

The acetone–butanol–ethanol (ABE) is considered as a promising biofuel to partially substitute the diesel fuel. In this paper, the optical constant volume combustion chamber was used to record the chamber pressure, and measured the soot mass and distribution for ABE and diesel blends. Then, the CFD KIVA-3V code coupled with the CANTERA was used to simulate the formation and oxidation processes of soot during the spray combustion. In addition, the CFD simulation cases for pure diesel and ABE20 were comprehensively validated against the experimental data under different initial ambient oxygen concentrations. Finally, a series of CFD cases were performed to investigate the effects of different ABE/diesel blends (up to 50% by volume), different initial ambient temperatures (mimic the traditional combustion and low temperature combustion modes) and oxygen concentrations (represent the free, low and high EGR conditions) on the combustion and soot formation characteristics under the diesel engine-relevant conditions. The results indicated that with the increase of ABE ratio in the ABE/diesel blends, the combustion pressure and heat release rate decreased and the combustion phase was delayed, the combustion temperature distribution was more uniform, while the flame lift-off length was increased gradually. In addition, the soot mass was decreased and its corresponding generation rate was also decreased with increasing the ABE ratio in blends. Furthermore, high concentration of soot mainly distributed in the temperature range of 1800–2000 K and the equivalent ratio range of 1.8–2.0.

Autoignition characteristics of diesel spray under different injection pressures and cold start strategy for compression ignition engines

Poor cold start performance is one of the main factors restricting the application range of compression ignition engines. Stable flame generation in the cylinder is the prerequisite for the successful start of the engine. In order to explore ways to improve the cold start ability of the compression ignition engine, the ignition characteristics of diesel sprays at different injection pressures were studied in a constant volume combustion chamber. A high-speed photography technique was used to obtain the color images of the initial flames of diesel free sprays. And the yellow flame is introduced as the criterion for a successful flame generation. It was found that under moderate injection pressures, the reactant concentration and energy dissipation rate reached equilibrium. Under this condition, the duration of the blue flame is relatively stable, and it is most conducive to the generation of the yellow flame in the cylinder. The negative temperature coefficient phenomenon is also observed, and the temperature range in which this phenomenon occurs is identical with the change of injection pressure. A cold start strategy for the compression ignition engine is proposed by controlling the compression-end temperature in the cylinder to be higher than the threshold ignition temperature of diesel spray.

Effect of the Plasma Jet Ignition and Flame Kernel Under The Combustion Process in a Constant Volume Combustion Chamber

This work is to study the plasma application using a capacitive discharge ignition capable of using the plasma jet which belongs to the non-thermal plasma physic. A plasma-jet spark plug was designed to combine a discharge chamber including an insulator and expanding the plasma area. The nonresistance was applied to acting the interference suppression of a plasma-jet spark plug to ensure the high energy generated at a DC-DC converter. An ANSYS FLUENT program was used to conduct analyzing combustion progress. The combustion simulation model is composed of configurations of a spark plug, a lambda sensor, and an internal combustion chamber. Resultantly, the minimum value of the combustion pressure is verified at λ = 1.6, and the plasma jet has higher values in the order of 2, 3, and 4 bar than the conventional models due to having a fast reaction. Consequently, the plasma jet has advantageous in combustion diffusivity in comparison to the conventional spark plug since the negative electrode of the cathode is not designed in front of a jet plug.

N-Butanol and Oleic Acid Methyl Ester, Combustion and NVH Characteristics In Reactivity Controlled Compression Ignition

Abstract Combustion, noise and vibrations produced by n-Butanol and Oleic Acid Methyl Ester (MO) in Reactivity Controlled Compression Ignition (RCCI) were investigated. The Cetane Number was determined using a Constant Volume Combustion Chamber (CVCC) for MO100, ULSD, and n-Butanol and found to be 73.8, 47.2, and 16 respectively. In the case of the MO20Bu80 (Methyl Oleate 20% with 80% n-butanol), the maximum Apparent Heat Release Rate was higher compared to ULSD Classical Diesel Combustion (CDC), due to accumulation of fuel in the combustion chamber because of the longer ignition delay and cylinder and charge cooling effect of n-butanol. RCCI with Methyl-Oleate had a vibrations level of as much 4.5 (m/s2) higher than ULSD in CDC up to 2k Hz. The sound level found by the Acoustic Array sound level for MO20Bu80 in combustion was 4 (dB) louder than ULSD in CDC. RCCI was found to have its own acoustic spectrum compared to CDC, and this is because of the wider range and higher sound levels produced by RCCI. The study suggests that MO can be used as a surrogate fuel for full body biodiesel in RCCI combustion.

Spray Auto-ignition Behaviors of Diesel and Jet Fuel at Reduced Oxygen Environments

ABSTRACT Spray auto-ignition behaviors of the RP-3 jet fuel were compared to those of a conventional diesel fuel on a constant-volume combustion chamber. The experiments were conducted at changed ambient temperatures and oxygen concentrations, with adjusted fuel injection pressure and duration as well. Compared to diesel fuel, the RP-3 jet fuel exhibits less auto-ignition propensity and lower burn rate, its ignition delay, and combustion delay times are more sensitive to the change in temperature and oxygen concentration, and more obviously staged heat releases and pressure rises are observed at lower oxygen ambience. Also, the peak heat release rate of diesel fuel exhibits an apparent non-monotonic trend versus increased temperature at high oxygen environments, due to the reduced premixed burn intensity with increased ambient temperature, while this non-monotonic trend for the RP-3 jet fuel is less significant, as the peak burn intensity is less influenced by changed ambient temperature. Finally, both elevated injection pressure and extended injection duration significantly reduce the combustion delay time at lower ambient oxygen concentrations, because the interval between the two-stage pressure rises, that occur at lower ambient oxygen environments, are apparently shortened.

Visualization Research on Low-Temperature Ignition and Combustion Characteristics of Diesel/Gasoline Blends Under Cold-Start Conditions

Abstract Although engines fueled with diesel/gasoline blends show excellent combustion and emission performance, its low-temperature flame development characteristics under cold-start conditions remain to be further verified. To clarify the details, experiments were conducted in an optical constant volume combustion chamber using Mie-scattering and direct photography methods at different ambient temperatures. Results show that the ignition delay of pure diesel during spray combustion shows a zero temperature coefficient (ZTC) region, and the addition of gasoline weakens the ZTC behavior until it disappears. The cool flame initiates the ignition, and the hot flame tends to far from the base of the cool flame as the gasoline content increases. In addition, the addition of gasoline to diesel increases the ratio of cool flames because the high evaporation reduces the temperature in the mixing zone, so only cool flame occurs in the G45 blends. Consequently, the total flame intensity presents an order of magnitude decrease. At lower ambient temperatures, the addition of gasoline significantly increases ignition instability. It is difficult to convert a cool flame into a hot flame due to the inhomogeneity of temperature and species field, which results in various unstable ignition phenomena, such as a short flash cool flame and intermittent cool and hot flame. Therefore, it is essential to directly target the cool flame and pay attention to the intrinsic mechanism of the evolution from the cool flame to the hot flame during the spray combustion process.

Effects of an injector cooling jacket on combustion characteristics of compressed-ignition sprays with a gasoline-hydrogenated catalytic biodiesel blend

The fuel properties in Gasoline Combustion ignition modes (GCI) have been adapted by mixing high reactivity fuels for improving poor combustion stability with pure gasoline. Precise control of the injector tip temperature, as well as the fuel temperature, are considered as the essential boundary conditions to conduct the fundamental investigation on combustion process of GCI spray. Therefore, the impacts of an injector cooling jacket on the spray and combustion developments of a mixture contains 60% gasoline and 40% hydrogenated catalytic biodiesel are studied using a constant volume combustion chamber (CVCC) working under GCI mode. A dummy injector is equipped with a thermocouple to measure the effects of the cooling jacket and ambient temperature on tip temperature. The Schlieren imaging and Diffused Background Illumination Extinction Imaging techniques are employed to visualize the reacting spray development and in-flame soot formation. The results illustrate that the injector tip temperature is well-controlled with aiding of the cooling jacket, which only increases by 35 K with increasing ambient temperature by 250 K. Furthermore, it is found from the optical experiments that the liquid length, ignition delay and lift-off length are enlarged for the cooling mode compared to that of the uncooled one. The cooling jacket also brings in a larger overlapping area between liquid length and flame lift-off length. However, the in-flame soot production for the cooling jacket is increased more than twice compared to that of the uncooled one.

Experimental Study on Spray Characteristics of Gasoline/Hydrogenated Catalytic Biodiesel under GCI Conditions

The new blended fuel (gasoline/hydrogenated catalytic biodiesel) is expected to address the cold start problem under low temperature of gasoline compression ignition due to its excellent ignition performance. Additionally, its spray behavior as the combustion boundary condition could have a direct impact on the characteristics of subsequent combustion. Therefore, the objective of this study is to reveal the effects of hydrogenated catalytic biodiesel/gasoline on the spray characteristics under various ambient conditions. As a significant index of spray characteristics, the spray penetration was achieved by applying Mie scattering methods under nonevaporation and evaporation conditions on a constant volume combustion chamber. In addition, the experimental results were compared against the calculated values of the models. As demonstrated by the results, a better spray performance can be achieved by the blended fuel than diesel and hydrogenated catalytic biodiesel. In respect of spray penetration, there is almost no difference among the three fuels under the ambient temperature of 323 K. Nevertheless, the blended fuel is lower than that of hydrogenated catalytic biodiesel and diesel when the ambient temperature is 434 K and 523 K. Moreover, the blended fuel is the first to reach the stable state, and the hydrogenated catalytic biodiesel is earlier than diesel for the spray penetration. Meanwhile, the spray model is identified as suitable for the blended fuel.

Macroscopic Spray Behavior of a Single-Hole Common Rail Diesel Injector Using Gasoline-Blended 5% Biodiesel

This research studies the macroscopic spray structure from a single-hole common rail diesel injector using gasoline-blended 5% biodiesel for use in compression ignition engines. To reduce the NOX/PM trade-off emissions, researchers are investigating gasoline used in compression ignition engines, called gasoline compression ignition. As a result that gasoline is injected directly into the combustion chamber, its spray field has a significant effect on combustion and emissions. Due to its low lubricity, gasoline is blended with biodiesel 5%, as a lubricity enhancer, to prevent the failure of the high-pressure injection system. The macroscopic spray structures of this gasoline blend were investigated Schlieren photography and planar laser-induced fluorescence-particle image velocimetry. Injection pressure was handled by a conventional common rail system, while ambient pressure was controlled by supplying nitrogen into the constant-volume combustion chamber. The effects of injection pressure and ambient pressure on the gasoline spray elucidated by Planar laser-induced fluorescence coupled with particle-image velocimetry (PLIF-PIV) imagery and comparisons with variations in neat diesel spray. In addition, the flow field of gasoline spray that formed vortexes and vorticity was characterized. The results show that the injection pressure and back pressure had the same effects on the gasoline spray structure, in terms of the penetration tip and cone angle, as on the diesel spray. However, the injection pressure had a greater effect on the diesel spray than the gasoline at low ambient pressure due to the occurrence of cavitation. Moreover, the images show the remarkable turbulent structure of gasoline spray and indicate air entrainment at the spray tip region.

Effects of branch structure of alkylbenzenes on spray auto-ignition of n-decane and alkylbenzenes blends

Spray auto-ignition characteristics of the blends of n-decane and several alkylbenzenes were carried out on a heated constant-volume spray combustion chamber. The derived cetane numbers of the fuel blends were determined, and the temperature-dependent ignition delay times and combustion durations were measured across a range of temperatures from 808 to 911 K. The results reveal that blending alkylbenzene to n-decane inhibits fuel spray auto-ignition propensity. For mono-alkylbenzenes, the fuel blend containing toluene has a higher derived cetane number than those with ethylbenzene and n-propylbenzene, but has a lower derived cetane number than the fuel blend containing n-butylbenzene. For those binary fuels containing ethylbenzene, n-propylbenzene and n-butylbenzene, their derived cetane numbers increase with the side alkyl chain length. The derived cetane numbers of the fuel blends with C8H10 isomers follow the trend of n-decane/ o-xylene > n-decane/ethylbenzene > n-decane/ m-xylene ∼ n-decane/ p-xylene, given the alkylbenzene blending fraction. For the blends with C9H12 isomers, those containing 1,2,3-trimethylbenzene and 1,3,5-trimethylbenzene have the highest and lowest derived cetane numbers, respectively, while the fuel blends containing 1,2,4-trimethylbenzene, n-propylbenzene and i-propylbenzene have comparatively intermediate derived cetane numbers. The blending effects of alkylbenzenes on ignition delay time are consistent with the observation on fuel derived cetane numbers. Both the number and proximity of substituted methyl groups significantly affect fuel auto-ignition propensity, and the adjacent methyl groups could increase the auto-ignition propensity. The combustion duration for the test fuels, except for n-decane and the n-decane/ n-butylbenzene blend, monotonically decreases with increased temperature. The non-monotonic dependence of combustion duration on temperature, for neat n-decane and the n-decane/ n-butylbenzene blend, may result from the increased diffusive burnt fraction. Finally, the comparison between gas-phase and spray auto-ignition reactivity of the test fuels highlights the contribution of both fuel physics and chemistry in spray auto-ignition.

Rate of heat release characteristics of supercritical sprays of dieseline blend in constant volume combustion chamber

In present experimental study, combustion characteristics of homogeneous supercritical (SC) fuel spray injection system are analyzed in cylindrical constant volume combustion chamber (CVCC) at experimental conditions similar to diesel engine-like operating conditions. A comparative study is also performed between SC fuel spray and normal diesel spray combustion under similar conditions. Combustion characteristics of SC fuel sprays includes rate of heat release (ROHR) and peak pressure (PP). Operating parameters include hot surface temperature range (673 ​K–723 ​K), pre-firing cylinder air pressure range (20 ​bar–40 ​bar) and injection pressure (IP) range of 100 ​bar–300 ​bar. Piezoresistive pressure transducer is employed for indicating and recording combustion processes. Diesel fuel and dieseline blend (50% gasoline and 50% diesel by v/v) are used for normal diesel spray and SC spray combustion respectively. It is found that ROHR in SC fuel spray combustion is smaller than in normal diesel spray combustion at all operating conditions. In SC fuel spray combustion, ROHR increases with increase in IP but decreases with increase in HST and CP due to homogeneous and hot air combustion nature of SC fuel sprays. Percentage reduction in ROHR of SC fuel spray combustion as compared to ROHR in normal diesel spray combustion is found to be nearly 34% at normal operating conditions of diesel engine. PP reached during SC spray combustion is noted to be less than PP reached during normal diesel spray combustion in all cases and is responsible for reduced NOx formation in SC spray combustion.

Explosion characteristics of hydrous bio-ethanol in oxygen-enriched air

Hydrous bio-ethanol is a promising alternative fuel, which consumes less energy during the production than anhydrous bio-ethanol. However, hydrous bio-ethanol features a slow burning rate, leading to low combustion stability, or even misfire especially at a high water content. Preliminary research has shown that oxygen-enriched combustion (oxy-combustion) effectively solves the slow burning rate issue. However, oxy-combustion might increase the potential explosion hazard. Therefore, it is essential to study the explosion characteristics of hydrous bio-ethanol oxy-combustion before its application in practical engines. In this paper, an explosion characteristic study of hydrous bio-ethanol was carried out in a constant volume combustion chamber (CVCC). Hydrous bio-ethanol with 20 vol% water (E80W20) was selected for the investigations considering the tradeoff between production energy saving and burn rate. The boundary conditions for the experiments are initial pressures of 1–4 bar, initial temperatures of 358–418 K, air with the oxygen concentrations of 21–25% and equivalence ratios of 0.7–1.4. Explosion parameters such as explosion pressure, maximum rate of pressure rise, deflagration index, and combustion duration were analyzed. The results showed that both the explosion pressure and maximum rate of pressure rise increased linearly with the initial pressure. Deflagration index increased linearly with the oxygen concentration but it was insensitive to the initial temperature. In most cases, the deflagration index was lower than 20 MPa·m/s, revealing that E80W20 is relatively safe when it is combusted with air with a 23% oxygen content. This work paves the way for the application of hydrous bio-ethanol oxy-combustion in practical engines.

Laminar Burning Velocity and Markstein Length of CH4/CO2/Air Premixed Flames at Various Equivalence Ratios and CO2 Concentrations Under Elevated Pressure

ABSTRACT Biogas is a renewable fuel predominantly composed of carbon dioxide (CO2) and methane (CH4) in varying proportions. The effects of the varying CO2 proportion need to be clarified for the development of engines. The laminar burning velocity and the burned gas Markstein length of premixed CH4/CO2/Air were measured with CO2 concentration ranging from 0.3 to 0.7 dilution ratios. The equivalence ratio was varied from 0.8 to 1.2, the initial pressure was set at 0.5 MPa, and the temperature was set to 298 K. The experiment was performed using a high-pressure constant volume combustion chamber. One-dimensional simulation of the flames was conducted using GRI-Mech 3.0. The results showed a reduction in the laminar burning velocity of CH4/CO2/Air mixtures with an increase in CO2 dilution ratio. A non-monotonic relationship was discovered between measured Markstein length and CO2 dilution ratio with different equivalence ratios. It was found that an increase in the CO2 dilution increased the response of the flames to stretch. For the lean and stoichiometric flames, the Markstein length was nearly constant with CO2 dilution of 0–0.5 and decreased with CO2 dilution of 0.7, suggesting an increase in susceptibility of the flame to the intrinsic flame instability. This was found to be mainly due to an increase in the Zel’dovich number and a decrease in the effective Lewis number with CO2 dilution. The Markstein length of the rich flame increased with CO2 dilution as it was more sensitive to CO2 dilution. Thermo-diffusive effects and pure stretch effects had similar influences on the burning velocity of the rich flames with an increase in stretch rate.

Fischer-Tropsch coal-to-liquid fuel negative temperature coefficient region (NTC) and low-temperature heat release (LTHR) in a constant volume combustion chamber (CVCC)

The purpose of the study was to investigate the correlation between thermal characteristics of neat Iso-Paraffinic Kerosene (IPK) in relation to Low Temperature Heat Release (LTHR), ignition delay, and combustion delay within the Negative Temperature Coefficient region (NTC), utilizing a Box-Behnken design matrix. There were 15 trials of 3 control input parameters which were strategic manipulations of ASTM standard D7668-14a. The standard parameters are: 1000 bar for injection pressure, a combustion chamber temperature of 595.5 °C, and an injection pulse width of 2.5 ms. It was observed that, at ASTM standard, the Derived Cetane Number of neat Ultra-Low Sulfur Diesel (ULSD) and IPK was 47.38 and 25.9, respectively. Results show that the LTHR duration and energy release were reduced when two parameters were simultaneously increased in ULSD operation. Meanwhile, for both fuels, the duration and energy release in LTHR has increased when two parameters were simultaneously reduced. It was found that the lower set wall temperature resulted in increased NTC region and LTHR increased to over 10% of the total energy release. The maximum combustion pressure for both ULSD and IPK where increased by 17.2% and 16.1% respectively from the standard due to the increase in injection pressure and pulse width.

Effect of O2 concentration in ambient mixture and multiphase radiation on pollutant formation in ECN spray-A

This study investigates the formation and evolution of soot and NO X in a high-pressure constant-volume combustion chamber. This work focuses on the effect of multiphase thermal radiation and O2 dilution in ambient/exhaust gases, sometimes also referred to as exhaust gas recirculation (EGR), qualitatively and quantitatively. The spray-A case (n-dodecane as fuel) from Engine Combustion Network (ECN) is used as the target condition. Two different soot modelling approaches have been considered: a semi-empirical two-equation model and a detailed method of moments with interpolative closure (MOMIC) model. A multiphase photon Monte Carlo (PMC) solver with line-by-line (LBL) spectral data is used to resolve radiative heat transfer. Results show that the effect of radiation on soot is minimal in spray-A. Inclusion of radiation modelling, on the other hand, marginally reduces NO prediction. Both peak soot and NO formation increase with O2 content in the ambient gas. Oxygen content in ambient gas is also found to have significant effect on soot sizes as the mean soot diameter increases along with considerable widening of the diameter distribution with the increase of O2 percentage in the ambient gas.

Autoignition study of LPG blends with diesel and HVO in a constant-volume combustion chamber

There is an increasing interest in reducing CO2 as far as it is the main responsible of greenhouse gas (GHG) emissions. Since the contribution of heavy-duty (HD) vehicles to GHG emissions of the road transport sector reaches 24% in the European Union, Liquefied Petroleum Gas (LPG) is suggested as a promising alternative fuel to be introduced in HD vehicles. The main drawback when using LPG in diesel engines is its poor autoignition behavior. To overcome this difficulty is possible to mix LPG with Hydrotreated Vegetable Oil (HVO) or diesel fuel, which acts as an ignition improver. This work has focused on LPG-HVO blends up to 75 %m/m LPG content, with lower LPG content admixtures included. Another measure to promote autoignition is using advanced injection strategies, particularly at low thermal conditions in the combustion chamber. This study concluded that 25LPG-75HVO blend (without any injection strategy modification) and 50LPG-50HVO blend (with advanced injection strategy) show better autoignition behavior than diesel fuel at low thermal conditions. At usual combustion conditions, LPG-HVO blends up to 75 %m/m LPG content can be supplied using an advanced injection strategy, and achieving similar autoignition behavior than diesel. LPG and HVO contents in the blend can be balanced depending on the thermal conditions. Therefore, a novel injection system with an in-line mixing valve capable of managing the instantaneous LPG/HVO ratio for compression ignition engines, is suggested. Testing these blends with advanced injection strategies using the in-line mixing system in a real HD engine would confirm these results.