Negative Valve Overlap Mode of HCCI Operation Using Gasoline and Diesel Blended Fuels

The negative valve overlap (NVO) strategy of HCCI operation was experimentally investigated on a gasoline HCCI engine operated with variable valve timing in association with the addition of diesel fuel. The experimental results show that, by using gasoline and diesel blended fuels, the required NVO interval for suitable HCCI combustion under a given engine speed and a moderate compression ratio condition could be reduced, and the HCCI combustion region was extended remarkably without substantial increase in NOx emissions under a given inlet and exhaust valve timing due to the improvement of charge ignitability. In addition, the possible scale of NVO was extended. A substantial increase in the lean limit of excess air ratio and the upper limit of load range can be achieved because of higher volumetric efficiency, resulting from the decrease in the required NVO and the presence of less residual gases in cylinder.

Multi-objective Design of Blending Fuel by Intelligent Optimization Algorithms

Fuel design is a complex multi-objective optimization problem in which facile and robust methods are urgently demanded.Herein,a complete workflow for designing a fuel blending scheme is presented,which is theoretically supported,efficient,and reliable.Based on the data distribution of the composition and properties of the blending fuels,a model of polynomial regression with appropriate hypothesis space was established.The parameters of the model were further optimized by different intelligence algorithms to achieve high-precision regression.Then,the design of a blending fuel was described as a multi-objective optimization problem,which was solved using a Nelder–Mead algorithm based on the concept of Pareto domination.Finally,the design of a target fuel was fully validated by experiments.This study provides new avenues for designing various blending fuels to meet the needs of next-generation engines.

Experimental Investigation on Macro Spray Characteristics of Octanol-Biodiesel-Diesel Ternary Fuel Blend

This study investigates the spray characteristics of ternary blends composed of octanol, biodiesel, and diesel fuel.Experiments are conducted using six materials to examine the variation in spray characteristic and to verify and compare a previously established spray tip penetration model with a modified model. The results show that the addition of OB100(30%of octanol, 70% of biodiesel) improves the spray characteristics of the fuel. Specifically, the addition of 10% or 20% of OB100 leads to a slight increase in the spray tip penetration, average spray cone angle, maximum spray width, and the spray area of the fuel blend;however, further addition of OB100 causes a corresponding decrease in these parameters. Based on previous research, this study uses kinematic viscosity instead of dynamic viscosity and density to modify the prediction model of spray tip penetration. The modified model exhibits a better fit quality and agreement with the experimental data,making it more suitable for predicting the spray tip penetration of fuel blends compared to the Hiroyasu-Arai model.

Preparation and emission characteristics of ethanol-diesel fuel blends

The preparation of ethanol-diesel fuel blends and their emission characteristics were investigated. Results showed the absolute ethanol can dissolve in diesel fuel at an arbitrary ratio and a small quantity of water(0.2%) addition can lead to the phase separation of blends. An organic additive was synthesized and it can develop the ability of resistance to water and maintain the stability of ethanol-diesel-trace amounts of water system. The emission characteristics of 10%, 20%, and 30% ethanol-diesel fuel blends, with or without additives, were compared with those of diesel fuel in a direct injection(DI) diesel engine. The experimental results indicated that the blend of ethanol with diesel fuel significantly reduced the concentrations of smoke, hydrocarbon(HC), and carbon monoxide(CO) in exhaust gas. Using 20% ethanol-diesel fuel blend with the additive of 2% of the total volume, the optimum mixing ratio was achieved, at which the bench diesel engine testing showed a significant decrease in exhaust gas. Bosch smoke number was reduced by 55%, HC emission by 70%, and CO emission by 45%, at 13 kW/1540 r/min. However, ethanol-diesel fuel blends produced a few ppm acetaldehydes and more ethanol in exhaust gas.

Autoignition of butanol isomers/n-heptane blend fuels on a rapid compression machine in N_2/O_2/Ar mixtures

Ignition delay times of butanol isomers/n-heptane mixture were measured using a rapid compression machine at compressed pressures of 15,20 and 30 bar,in the compressed temperature range of 650–830 K and equivalence ratio of 1.0.Sensitivity analysis and reaction fluxes analysis were performed using a detailed mechanism of blend fuels so as to evaluate the impact of n-heptane addition and temperature variation on the ignition and combustion process.Over the experimental conditions in this study,the blend fuels displays apparent low and high temperature reactions and a negative-temperature-coefficient(NTC)behavior.With increasing butanol isomers mole fraction in the mixtures,the ignition delay times increase.It is worth noting that the suppression to n-heptane ignition from tert-butanol is very limited.The ignition delay time of 40/60 tert-butanol/n-heptane mixture is smaller than other three kinds of blends.With the increasing of tert-butanol mole fraction,the increasing range of its ignition delay time is very large.Moreover,compressed pressure has a limited effect on the ignition of blend mixture at low temperature but certain influence at medium temperature arrange.Tert-butanol/n-heptane mixture is not sensitive to the pressure.The chemical analysis indicates that butanol isomers also present the NTC behavior because of the low temperature reactivity radicals pool produced by n-heptane.Reaction fluxes analysis shows that the n-heptane addition has little impact on the reaction path.Sensitivity analysis shows that for the pure n-butanol,2-butanol and iso-butanol fuel,H-abstraction from the?-carbon plays the dominant role in the reactions having the inhibiting effect on the low-temperature branching,while the H-abstraction from the?-carbon can promote the ignition;for tert-butanol/n-heptane mixtures,reaction R16.H2O2(+M)<=>OH+OH(+M)plays the leading role.For n-butanol/n-heptane,iso-butanol/n-heptane mixtures,the major promoting reactions include some H-abstraction from n-heptane and OH branching reactions,the influence of H-abstraction from?-carbon is weaken;For 2-butanol/n-heptane,tert-butanol/n-heptane mixtures,R16 plays an absolutely dominant role,while the major inhibiting reactions add some elementary reactions of small radicals.

Experimental Investigation of the Rail Pressure Fluctuations Correlated with Fuel Properties and Injection Settings

Injection-induced rail pressure fluctuations are proven to cause nonuniform spray development.These fluctuations are also responsible for generating lower injection pressures,to the detriment of jet penetration length and break-up timing.Despite the vast literature dealing with such issues,several aspects of rail pressure fluctuations remain unclear.Additionally,the need for compliance with the emission legislation has shed light on the potential of alternative fuels,which represent a pathway for sustainable mobility.This scenario has motivated the present study dealing with the assessment of the time history of rail pressure correlated with fuel properties.Tests have been performed using a last-generation common rail injection equipment under various injection settings,employing diesel and 2-methylfuran-diesel blend.This paper describes the research activity and aims to provide new insights into the correlation of rail pressure fluctuations with fuel properties.

Stable Combustion under Carbon Dioxide Enriched Methane Blends For Exhaust Gas Recirculation(EGR)

Exhaust gas recirculation(EGR)is one of the main techniques to enable the use of oxyfuel combustion for carbon capture and storage(CCS).However,the use of recirculated streams with elevated carbon dioxide poses different challenges.Thus,more research is required about the cumulative effects on the desirable outcomes of the combustion processes such as thermal efficiency,reduced emissions and system operability,when fuels with high CO_(2) concentration for CCS exhaust gas recirculation or biogas are used.Therefore,this study evaluates the use of various CO_(2) enriched methane blends and their response towards the formation of a great variety of structures that appear in swirling flows,which are the main mechanism for combustion control in current gas turbines systems.The study uses 100 kW acoustically excited swirl-stabilised burner to investigate the flow field response to the resultant effects of the variation in the swirl strength,excitation under isothermal condition and the corresponding effects during combustion with different fuels at various CO_(2) concentrations.Results show changes in size and location of flow structures as a result of the changes in the mean and turbulent velocities of the flow field,consequence of the imposition of different swirl and forcing conditions.Improved thermal efficiency is also observed in the system when using high swirl and forcing while the blend of CO_(2) with methane balanced the heat release fluctuation with a corresponding reduction in the acoustic amplitudes of the combustion response,suggesting that certain CO_(2) concentrations in the fuel can provide more stable flames.Concentrations between 10%to 15%CO_(2) volume show great promise for stability improvement,with the potential of using these findings in larger units that employ CCS technologies.