Higher Heat Release Rate Research Articles

Combustion performance and emission characteristics on HCCI engine of waste plastic pyrolysis oil biodiesel blends with external PFI and vaporiser

ABSTRACT Analysis of plastic oil obtained from waste plastic through pyrolysis process, as an alternative to biodiesel is presented in this paper. The HCCI engine is considered for experimental validation of combustion performance and emission characteristics. To accumulate pyrolysis oil as fuel, the design modifications were made in external mixture formation on the existing computerised 4-stroke, single cylinder, water cooled, direct injection kirloskar diesel engine connected with eddy current dynamometer to satisfy HCCI conditions. HCCI engine can be worked on wide assortment of fuels beginning from diesel to different blends (WPPO 5%,10%,15% and 20% by volume) of biodiesel .The designed additional device connected to the engine is utilised for fuel vaporisation and mixture arrangement. In the experimental study, the combustion results were initiate to be of 39.69 % higher Rate of Heat Release (RoHR) for biodiesel HCCI as compared with diesel HCCI. Higher brake thermal efficiency (BTE) was found 37 % without exhaust gas recirculation (EGR) at WPPO 20 % biodiesel blend. And also found 50 % and 65 % reduction in NOx emission and 18 % and 28 % reduction in smoke opacity are obtained for biodiesel vapour induction without EGR and biodiesel vapour induction with 15 % EGR as compared with diesel fuel. The CO (0.34 %), and UHC (2.15 %) emissions are increases with 15 % EGR, but the emissions are within the standard limits specified by the emissions standards.

Characteristics of microalgae spirulina biodiesel with the impact of n-butanol addition on a CI engine

The aim of the present study is to investigate the effect of ternary blends of n-butanol-spirulina microalgae biodiesel and diesel fuel on compression ignition engine characteristics. Investigation was performed comparing n-butanol blended with microalgae spirulina biodiesel (MSB), low sulphur diesel and pure biodiesel at different engine loads. The MSB (40, 30 and 20%) – n butanol (10, 20 and 30%) blends were 50% with low sulphur diesel fuel in volume basis as B1 (LSD50-MSB40-nB10), B2 (LSD50-MSB30-nB20) and B3 (LSD50-MSB20-nB30). The comparison was made with diesel, biodiesel and n-butanol blended fuels which shows a reduction in exhaust gas temperature, Bosch smoke number (BSN), and brake specific particulate matter (BSPM) emission while showing higher specific fuel consumption (SFC), carbon dioxide, and nitrogen oxides emissions. The B20 blend led to a slight reduction in BTE (0.75%), NOX emission (12.58%), BSN (8.95%), and BSPM emission (31.88%) while increasing SFC as compared to diesel fuel. With the addition of the n-butanol in the diesel - microalgae spirulina biodiesel blends, brake thermal efficiency (BTE) has significantly improved during higher heat release rate and cylinder pressure while reduction in smoke and BSPM emissions at all engine loads for B1, B2 and B3 blends.

Effects of cavity depth on the ethylene-air Continuous Rotating Detonation

Continuous Rotating Detonation (CRD) is a promising combustion mode for aerospace propulsion, with high heat release rate and thermodynamic efficiency, but it exhibits realization difficulty for fuels with low chemical activity. To settle this issue, a cavity-based annular combustor scheme has been proposed in our previous study, and its feasibility has been well demonstrated. A series of ethylene-air tests under different cavity configurations have been carried out in this paper, and the effects of cavity depth are revealed. For CRD mode, traditional isobaric combustion also exists at the contact surface between the high temperature burnt products and combustible mixture. Increasing the cavity depth can improve its isobaric combustion holding ability, but excessive isobaric combustion could destroy the foundation of CRD. For fuels with low chemical activity, appropriately improving the isobaric combustion can help the CRD realization. This paper reveals the cavity depth effects on the competitive relationship between isobaric combustion and CRD, and it can be used as a guideline for the CRD combustor design.

Performance, Emission and Combustion Characteristics of VCR CRDI Diesel Engine Fuelled with n-butanol Blends

This research work indicates the analysis conducted to investigate the performance, exhaust emission and combustion characteristics of a VCR diesel engine fuelled with nbutanol blends at a rated speed of 1500 rpm with 300 bar injection pressure at compression ratios of 16, 18 and 20. The test fuel was prepared by adding n-butanol 10% (NB10) and 20% (NB20) to diesel by volume. The combustion characteristics investigated were; rise in-cylinder pressures, net heat release rate, cumulative heat release rate and mass fraction of fuel burned at all loads using three compression ratios. The emission and performance study also conducted. The higher heat release rates, increased cylinder pressures were observed for both the blends compared to diesel. Increased brake thermal efficiency observed at higher compression ratio for NB20 blend. It had also been observed that the emissions of CO2, HC and NOx were increased for both the blends, while CO emissions decreased in trend with an increase in compression ratio and blend strength.

Effect of injection pressure on the combustion, performance and emission characteristics of a biodiesel engine with cerium oxide nanoparticle additive

Vegetable oil based fuels are promising substitutes for diesel fuel for transport and industrial applications. Converting raw vegetable oils into their ethyl or methyl esters has reasonably solved the problems associated with their high viscosities. The purpose of the research is to investigate experimentally the effect of injection pressure on the combustion characteristics of a biodiesel engine using cerium oxide nanoparticles as a fuel additive. Biodiesel derived from waste cooking oil mixed with mineral diesel in the proportion 20:80 is used along with cerium oxide (CeO2) nanoparticles as additives. The engine is run at several fuel injection pressures (180, 210 and 240 bar) and with a nanoparticle concentration of 80 ppm. The experiments demonstrate that the higher injection pressure associated with nanoparticle addition improves engine combustion characteristics, e.g., it leads to a higher peak pressure and a higher heat release rate. The best performance was observed at an injection pressure of 240 bar with a 80 ppm nanoparticle concentration. Concentrations of hydrocarbon, oxides of nitrogen and smoke decreased for higher injection pressures with nanoparticle addition. Hence an enhancement in engine performance and decrease in emissions can be achieved in a biodiesel engine by employing higher injection pressures with nanometer sized cerium oxide particles as additives. This helps in conserving the petroleum based fuels and also avoiding the emissions of contaminants to the atmosphere.

Design of fire scenarios for Australian underground hard rock mines – Applying data from full-scale fire experiments

One of the most significant tools when designing fire safety in an underground mine is the design fire methodology. This paper presents a number of design fire scenarios which were developed from risk assessments and risk analysis where a deterministic approach was implemented and where the results from earlier full-scale fire experiments in underground mines and analysis were included in the process. The developed scenarios showed that for scenarios, in which ventilation flow was in the same direction as the fuel continuity, continued fire spread to all major components were provided and longer and intermittent periods which resulted in high heat release rates resulted, would present a considerable risk to underground personnel. It was also found that the inclination of the decline has little influence on the resulting heat release rate – despite the flame tilt – and that the design of the mining vehicles was found to effectively delay or even prevent the ignition of adjacent fuel items in a number of cases. The design fire scenarios developed will provide a key tool when evaluating fire protection measures in an underground mine. • The most rapid initial fire growth scenarios presented a risk during evacuation. • The inclination of the decline had little effect on the heat release rate curve. • Delayed, sudden increase of heat release rate posed a risk during rescue operations.

Effects of late injection on lean combustion characteristics of methane in a high compression ratio optical engine

Energy crisis and environment pollution have made engines fueled with natural gas getting more and more attention, but practical engines fueled with natural gas often suffer from low engine power output and thermal efficiency. In this study, with addressing the role of late high-pressure injection, engine performance and flame propagation were studied in a high compression-ratio optical engine fueled with methane under lean combustion condition. First, the experiments with different excess air coefficients under two representative injection timing conditions were performed. The results show that with the increase of excess air coefficient, the indicated mean effective pressure (IMEP) is decreased. When the excess air coefficient is high, the combustion even becomes unstable under early injection conditions, which is due to the low flame speed. Second, different injection timings were employed under lean condition, and the results show that the combustion process is significantly affected by injection timing. Advanced combustion phase and higher heat release rate are observed under late injection condition. Finally, further analysis of flame images and pressure shows that late injection can increase the air intake quantity but also in-cylinder turbulence intensity. The highest flame speed is obtained under the latest injection condition with an increment above 50%, and flame propagation direction is also changed under different injection timings. Besides the compression pressure before spark is higher for late injection, meaning high volumetric efficiency. Therefore, late injection with high pressure is an effective way to improve the power output and thermal efficiency of natural gas engine.

Hydration of ternary Portland cement blends containing metakaolin and sodium bentonite

Although metakaolin can enhance the hydration of cement, its pozzolanic reactions occur primarily at the early age with a high heat-release rate and low degree of reaction resulting in a reduction in the composite strength especially at high substitution levels. To address this challenge, a combination of metakaolin and sodium-bentonite is adopted as a partial replacement of cement. The influence of coupled substitutions of these two clays on hydration of Portland cement is investigated by characterizing hydration kinetics and products related to microstructural and physico-chemical parameters. The results indicate that the coexistence of sodium-bentonite and metakaolin enhances the cement hydration in terms of strength development, portlandite consumption and formation of supplementary calcium silicate hydrate (C-S-H) phases with elongated molecular chain lengths. Dissolution of metakaolin is increased in the presence of bentonite. It was found that the conversion of ettringite to monosulfate, the formation of strätlingite, and the length of aluminosilicate chains increase with increasing Al/Si ratio, which is related to the amount of dissolved metakaolin. A thermodynamic simulation is also presented to support these findings.

Numerical analysis of knocking characteristics and heat release under different turbulence intensities in a gasoline engine

In this work, different knocking characteristics and heat release have been numerically studied in a downsized spark-ignition engine, with addressing turbulence intensity and spark-ignition timing. The results show that knock intensity mainly depends on the heat release of hot-spots, and the heat release is not only associated with unburned mass fraction but also closely related to subsequent autoignition development processes, e.g. end-gas autoignition mode. Under low turbulence intensity, local mixture autoignition is induced by a single hot-spot, accompanied by an autoignition reaction wave propagation; whereas under high turbulence intensity, a nearly homogeneous autoignition event characterizing quasi constant-volume combustion is observed. Meanwhile, compared with the single hot-spot autoignition, the homogeneous one can lead to more intensive local overpressure and thus stronger knock intensity. Further analysis on the underlying reasons shows that the higher heat release rate under homogeneous autoignition conditions is the main reason for the stronger knock intensity. Besides, the dependency of knock intensity and heat release on unburned mass fraction is found effective only for the same autoignition scenarios. Current study can provide insights into knocking suppression with consideration of intake system optimization in modern downsized gasoline engines.

Influence of Injection Timing on Performance and Exhaust Emission of CI Engine Fuelled with Butanol-Diesel Using a 1D GT-Power Model

Injection timing variations have a significant effect on the performance and pollutant formation in diesel engines. Numerical study was conducted to investigate the impact of injection timing on engine performance and pollutants in a six-cylinder turbocharged diesel engine. Diesel fuel with different amounts (5%, 15%, and 25% by volume) of n-butanol was used. Simulations were performed at four distinct injection timings (5°, 10°, 20°, 25°CA bTDC) and two distinct loads of brake mean effective pressure (BMEP = 4.5 bar and 10.5 bar) at constant engine speed (1800 rpm) using the GT-Power computational simulation package. The primary objective of this research is to determine the optimum injection timing and optimum blending ratio for improved efficiencies and reduced emissions. Notable improvements in engine performance and pollutant trends were observed for butanol-diesel blends. The addition of butanol to diesel fuel has greatly diminished NOX and CO pollutants but it elevated HC and CO2 emissions. Retarded injection timing decreased NOX and CO2 pollutants while HC and CO2 emissions increased. The results also indicated that early injection timings (20°CA bTDC and 25°CA bTDC) lowered both CO2 and unburned hydrocarbon emissions. Moreover, advanced injection timing slightly improved brake thermal efficiency (BTE) for all engine loads. It is concluded that retarded injection timing, i.e., 10°CA bTDC demonstrated optimum results in terms of performance, combustion and emissions and among the fuels 15B showed good outcome with regard to BTE, higher heat release rate, and lower pollution of HC, CO, and NOx.

Synthesis of new aromatic polyamides containing α-amino phosphonate with high thermal stability and low heat release rate

The new aromatic polyamides containing α-amino phosphonate were synthesized from phosphorus-based dicarboxylic acid 4 and various aromatic diamines by direct polycondensation reaction. Dicarboxylic acid 4 was successfully synthesized from trimethyl phosphite, 4-aminobenzoic acid and terephthaldehyde via a three-component reaction. The polymerization reaction produced the polyamides 6a–f with high yield and desirable inherent viscosities. The thermal properties of the all samples were investigated by thermo-gravimetric analysis (TGA). The TGA results in N2 exhibited the 10% mass loss temperatures (T10) in the ranges of 324–345 °C, while the T10 resulted from thermo-oxidative degradation were higher than those. The main data obtained by microscale combustion calorimetry revealed acceptable combustion properties such as very low peak of heat release rate for the synthesized polyamides 6a–f. The all of the results indicated that these polyamides can be potentially utilized as additive for improvement of thermal resistance and combustion behavior of thermoplastic materials.

Investigation of fire-driven cross-wind velocity enhancement

Understanding the aerodynamics associated with the interaction of fire and cross-wind flow is of great importance because the consequence may have major implications in building design against bushfire (or wildland fire) attacks. However, a fundamental understanding of how the interaction of fire and wind can alter free stream flow aerodynamic properties has remained elusive. The scope of this study is to examine the pool fire and wind interaction under fixed wind velocity condition. This study dissects the fundamental mechanisms of how the interaction of horizontal momentum flow with a vertical buoyant plume leads to enhancement of wind velocity in the horizontal direction at a certain elevation. Changes in flow aerodynamics caused by the interaction of fire and wind were analysed using the computational fluid dynamics approach. The mechanisms causing the changes were explained. A module was developed and added to the FireFOAM solver to evaluate flow acceleration due to the pressure gradient, gravity, and viscous effects. The chosen computational model was validated against two sets of experimental data, namely, a buoyant diffusion fire plume in still air and the other in cross-wind condition. The numerical simulation revealed that due to the interaction of fire and wind, there is a negative longitudinal pressure gradient across the plume axis, causing the flow to accelerate and the velocity profile to alter. It was also shown that the distortion in velocity profile depends on the location downstream of the fire plume. The height of the distortion increases whilst the magnitude of the distortion diminishes as the longitudinal distance from the fire source increases. Investigation of the effects of heat release rate on wind enhancement further showed that fire with a higher heat release rate causes a greater pressure gradient and a lower density, culminating in higher flow acceleration and consequently increase of wind enhancement.

Influence of hydrogen as a fuel additive on combustion and emissions characteristics of a free piston engine

It has been shown that using fuel additives play an important role in enhancing the combustion characteristics in terms of efficiency and emissions. In addition, free piston engines have shown capable in reducing energy losses and presenting more efficient and reliable engines. In this context, the objective of the present work is to investigate the effect of using hydrogen as a fuel additive in natural gas homogeneous charge compression ignition free piston engine. To this aim, two models have been iteratively coupled: the combustion model that is used to calculate the heat release of the combustion and the scavenging model that is employed to determine the in-cylinder mixture state after scavenging in terms of its homogeneity and species mass fractions and to obtain the finial pressure and temperature of the in-cylinder mixture. In the former model, the 0-D approach through Cantera toolkit has been considered due to the fact that homogeneous charge compression ignition combustion is very rapid and the fuel-air mixture is well-homogenous, whereas in the latter model, 3-D-CFD approach through AN-SYS FLUENT software is considered to ensure precise calculations of the species exchange at the end of each engine cycle. The effect of hydrogen as a fuel additive has been quantified in terms of the combustion characteristics (e. g., ignition delay, heat release rate, engine overall efficiency and emissions, etc.). It has been shown that hydrogen addition reduces ignition delay time, decreases the in-cylinder peak pressure, while allowing the engine to operate with higher mechanical efficiency as it has high heat release rate, increases the NOx emission levels of the engine, but decreases the CO levels

Effects of Turbulence Intensity and Biogas Composition on the Localized Forced Ignition of Turbulent Mixing Layers

ABSTRACTThree-dimensional compressible Direct Numerical Simulations (DNS) have been used to investigate the localized forced ignition of statistically planar mixing layers of biogas/air mixtures for different levels of turbulence intensity and biogas composition. The biogas is represented by a CH/CO mixture and a two-step mechanism involving incomplete oxidation of CH to CO and HO, and an equilibrium between the CO oxidation and the CO dissociation has been used. This two-step mechanism captures the variation of the unstrained laminar flame speed with equivalence ratio and CO dilution with sufficient accuracy when compared with detailed chemistry results. A successful ignition of CH/CO/air mixing layer initially gives rise to a tribrachial flame structure involving fuel-rich and lean premixed branches on either side of the diffusion flame stabilized on the stoichiometric mixture fraction iso-surface. Long after the energy deposition has ended, the lean branch may merge with the diffusion flame, but edge flame propagation along the stoichiometric mixture fraction iso-surface is observed at all stages. The highest heat release rate (HRR) is obtained on the rich premixed branch irrespective of the turbulence intensity and biogas composition, but its magnitude decreases with increasing CO dilution. The most probable edge flame displacement speed decreases in time and converges to its theoretical value for laminar cases. As the turbulence level increases, the edge flame displacement speed assumes a larger range of values, although its mean is consistently lower than the corresponding laminar one. Furthermore, in the turbulent cases, the probability of finding negative values of the edge flame displacement speed has been found to be non-zero. This probability is larger than the one of finding positive values for the cases failing to reach a self-sustained flame propagation without the energy deposition assistance. This becomes more probable as the turbulence intensity and CO dilution increase. This is reflected in the diminished burning extent, quantified in terms of burned gas volume, with increasing turbulence intensity and CO dilution.

Effect of engine size, speed, and dilution method on thermal stratification of premixed homogeneous charge compression–ignition engines: A large eddy simulation study

High heat release rates limit the operating range of homogeneous charge compression–ignition engines to low and medium loads. Thermal stratification has been shown to stagger autoignition, lower heat release rates, and extend the operating range of homogeneous charge compression–ignition engines. However, the dependence of naturally occurring thermal stratification on the engine size, speed, and internal residual dilution is not fully understood. A three-dimensional computational fluid dynamics model with large eddy simulations and detailed chemical kinetics was developed using CONVERGE. This model was used to simulate two different engines: (1) a light-duty 2.0 GM Ecotec Engine modified for homogeneous charge compression–ignition combustion in one of the cylinders and (2) a medium-duty Cummins B-series engine modified for homogeneous charge compression–ignition combustion in one of the cylinders. For the light-duty engine, five consecutive modeled cycles were compared with experimental data from 300 consecutive cycles using residual gas dilution at 2000 r/min. For the medium-duty engine, five consecutive modeled cycles were compared with experimental data from 100 consecutive cycles using air dilution with intake heating at 1200 r/min. In the light-duty engine, it was found that incomplete mixing between fresh charge and residual gas increased thermal stratification early in the compression stroke for residual dilution compared to air dilution. Residual stratification at the onset of ignition was small and not directly coupled with thermal stratification. Heat losses to the walls were the dominant source of thermal stratification at the onset of ignition. The reduced oxygen concentration due to residual dilution, increased the temperature requirement for autoignition, which increased heat transfer losses and increased the thermal stratification around top dead center. The thermal stratification before ignition reduced when the engine speed increased because of the lower heat transfer losses. The light-duty engine was found to have larger portion of the fuel energy lost to heat transfer than the medium-duty engine, which resulted in larger thermal stratification before ignition.

Autoignition-cascade in the windward mixing layer of a premixed jet in hot vitiated crossflow

This numerical study builds upon the experimental work of Wagner et al., e.g. [Combust. Flame 176 (2017)], and focuses on the flame stabilization mechanism of a reactive jet in crossflow (RJICF). A 300 K premixed ethylene-air jet (ϕj=1.2) is injected into a hot vitiated crossflow at 1500 K. A compressible three-dimensional (3-D) large eddy simulation (LES) was performed with an analytically reduced chemistry mechanism. Comparisons between LES and experiments are in good agreement in terms of jet trajectories and flow velocities. The LES captures the flame-flow interactions that were experimentally observed in the central plane of the RJICF by means of particle image velocimetry and OH planar laser-induced fluorescence. It gives access to the spatio-temporal evolution of the autoignition process along the windward mixing layer of the RJICF. Chemical explosive mode analysis shows that autoignition is the dominant flame stabilization mechanism on the windward side of the jet. “Low-heat-release” autoignition starts at the front root of the jet, at the “very lean” most reactive mixture fraction, which is the spot where the autoignition time of the mixture is the smallest. Immediately downstream, the released heat is advected and diffuses, contributing to a decrease of autoignition times in the neighboring richer inner side of the jet. Autoignition in this richer layer of the jet is characterized by higher heat release rate that again diffuses toward even richer regions until the stoichiometric layer ignites. This autoignition-cascade mechanism determines the position of the “visible” windward flame. Moreover, a 3-D flame analysis shows that the resulting “high-heat-release” autoignition patches expand within the stoichiometric layer and ultimately merge with the leeward propagating flame while being advected toward the flame tip. It is also shown that the latter layer, and therefore the growing autoignition patches, get wrinkled by the coherent structures that originate from the hydrodynamically unstable front root of the jet in crossflow.

A new concept of actively controlled rate of diesel combustion (ACCORDIC): Part II—simultaneous improvements in brake thermal efficiency and heat loss with modified nozzles

A new diffusion-based combustion concept (named it as Actively Controlled Rate of Diesel Combustion) for the confirmation of brake thermal efficiency optimum heat release rate profile based on multiple fuel injectors has been investigated. The outstanding results are; it is possible to achieve desired heat release rate profile only by the independent control of injection timing and duration of three injectors installed to a cylinder. The optimum brake thermal efficiency was not achieved with the Otto-like cycle but with the Sabathe-like cycle as predicted by a zero-dimensional thermodynamic model. Furthermore, smoke emissions were concurrently reduced with NOx emissions by increasing fuel amount from the side injectors without any deterioration in CO and total hydrocarbon emissions. On the other hand, brake thermal efficiency itself was not so improved than expected, because of lower heat release in the late part of combustion and unexpected less heat loss reduction. To solve these issues, combustion visualization and numerical simulation analysis were carried out. The results suggested that the adjacent sprays with narrower angle from each side injector deteriorated air entrainment and mixture formation, which might also result in the deterioration in wall heat loss in the expansion stroke. To solve both issues simultaneously, modified nozzle to inject against the swirl from the side injectors was utilized and achieved an improvement in both brake thermal efficiency and heat loss. That is the interdependent and reciprocal control of in-cylinder flow and fuel injection will be one of the breakthrough technologies for current trade-offs by the temporal and spatial spray flame optimization. Furthermore, the nozzle having higher flow rate with less number of orifice was utilized for the side injectors. Even though the smoke emissions were not optimized yet, brake thermal efficiency was much improved with higher heat release rate in the late part of combustion.

Eco-Friendly Flame-Retardant Additives for Polyurethane Foams: A Short Review

Polyurethane (PU) materials are extensively used in the construction industry as core material insulation for sandwich panel application, such as wall cladding, structure insulation and roof panel. Demands on PU application have escalated given its significant advantages to reduce energy consumption. Meanwhile, rigid PU (RPU) foams are combustible materials characterized by rapid flame spread, high heat-release rates, and ability to produce large quantities of toxic gases in original form. Thus, flame-retardant (FR) additives are used to improve the thermal properties of PU. However, some commercial additives used today have are hazardous to humans and the environment, and their extensive application is limited by their negative effects on polymer mechanical properties. Accordingly, identifying materials that are environmentally friendly and harmless to humans has become urgent. Some alternative additives that are gaining research interest are clay and fly ash, which are natural and recyclable resources that can enhance the FR properties of other polymers. However, room for improvement is always present as the related technology is continually being developed. This review focuses on studies aiming to enhance the flame retardancy of RPU foam using fly ash and local clay as additives.

Engine performance, emission and bio characteristics of rice bran oil derived biodiesel blends

The present work involves the investigation of biodiesel characteristics derived from rice bran oil via heterogeneous basic catalytic transesterification path as the rice husk contains about 16–20% of crude rice bran oil by its weight. Engine performance and emission characteristics of rice bran oil derived biodiesel blends during fueling a four-stroke, single-cylinder, direct-injection engine at 1500 rpm were investigated. The results indicate that 20% biodiesel blend leads to a lower ignition delay at higher loads which in turn increases the rate of vaporization of the fuel as it has higher cetane umber. This fuel blend has a high in-cylinder peak pressure and heat release rate (HRR) of about 72.1 bar and 70.826 J/°CA respectively, during the pre-mixed combustion phase in rapid combustion due to the higher oxygen content. Even though, it has high viscous nature, it possesses highest brake thermal efficiency (BTE) which adds absolute combustion. The exhaust gas temperature (EGT: 7.8221%) increases with load and the observed values were matched with other biofuels. Moreover, the HCs, COx and NOx emissions decrease as the load increases since the increase in fuel atomization promotes the combustion process and thereby decreases the amount of unburnt biodiesel components. At 100% load, the smoke cloudiness level was decreased by about 21.62%. The rice bran oil and the blended (20, 30 and 40%: B20, B30 and B40) samples were tested for their notable in vitro microbial, antioxidant and nuclease bio activities due to the presence of certain bioactive components in the rice bran derived biodiesel. If the rice bran oil (RBO) is converted effectively into biodiesel, thereby it will not only satisfy 60–70% of our diesel requirement but also facilitate a green environment.

Study on the flame development patterns and flame speeds from homogeneous charge to stratified charge by fueling n-heptane in an optical engine

The operation range of some new compression ignition (CI) combustion modes was extended compared to that of HCCI because of fuel stratification. Few researches tried to analyze the mechanism by comparison of flame development patterns and flame speed under different stratified conditions. In this work, high-speed imaging of natural flame luminosity was used to study the combustion process from homogeneous charge to stratified charge with a higher frame rate. Different stratification conditions were formed by adjusting the injection timings. Results show that the proportion of flame propagation increases and combustion reaction rate decreases as fuel distribution in cylinder changes from homogeneous charge to stratified charge. Flame propagation of auto-ignition kernel exists although the combustion is dominated by multipoint auto-ignition in HCCI combustion. The flame spreading speed is much higher than the flame speed because the fictitious reaction front is shorter than the actual reaction front for flame spreading speed calculation. Four principles are proposed for equivalent radius method to get more reasonable results of flame speed. For conditions that do not satisfy these principles, effective front method can be used. Flame speed in CI combustion modes is in the range of 10–50 m/s depending on different stratification conditions in current study. There is a good correlation between the flame speed and the peak heat release rate as SOI is retarded, i.e., high flame speed corresponds to high peak heat release rate. It can be concluded that controlling fuel stratification is an effective method to regulate the ratio between auto-ignition and flame propagation and achieve effective control on combustion reaction rate.