Effects of applying a Miller cycle with split injection on engine performance and knock resistance in a downsized gasoline engine

Wei, Haiqiao; Shao, Aifang; Hua, Jianxiong; Zhou, Lei; Feng, Dengquan

doi:10.1016/j.fuel.2017.11.006

Cited by 74 publications

(27 citation statements)

References 26 publications

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“…Because end-gas auto-ignition is the first stage of knocking, whose subsequent development determines the knocking occurrence and intensity, in general, it can be concluded that knocking in SI engines is induced by auto-ignition occurring in the end gas [3,4], which has been extensively and comprehensively investigated. Many excellent studies have contributed to exploring the method of inhibiting such knocking, and several potential means have been discovered, including changing the flame propagation speed [5], increasing the in-cylinder turbulence [6,7], split injection strategies [8], octane number [9,10], and EGR (Exhaust Gas Recirculation) strategies [11]. For instance, Yang et al [12] found a higher tumble rate can lead to the increase of flame speed through by facilitating the interaction between the fuel spray and air flow and the heat-mass transfer between the unburnt and burnt zone.…”

Section: Of 23mentioning

confidence: 99%

Effects of Flame Propagation Velocity and Turbulence Intensity on End-Gas Auto-Ignition in a Spark Ignition Gasoline Engine

et al. 2020

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Knocking is a destructive and abnormal combustion phenomenon that hinders modern spark ignition (SI) engine technologies. However, the in-depth mechanism of a single-factor influence on knocking has not been well studied. Thus, the major aim of the present study is to study the effects of flame propagation velocity and turbulence intensity on end-gas auto-ignition through a large eddy simulation (LES) and a decoupling methodology in a downsized gasoline engine. The mechanisms of end-gas auto-ignition as well as strong pressure oscillation are qualitatively analyzed. It is observed that both flame propagation velocity and turbulence have a non-monotonic effect on knocking intensity. The competitive relationship between flame propagation velocity and ignition delay of the end gas is the primary reason responding to this phenomenon. A higher flame speed leads to an increase in the heat release rate in the cylinder, and consequently, quicker increases in the temperature and pressure of the unburned end-gas mixture are obtained, leading to end-gas auto-ignition. Further, the coupling of a pressure wave and an auto-ignition flame front results in super-knocking with a maximum peak of pressure of 31 MPa. Although the turbulence indirectly influences the end-gas auto-ignition by affecting the flame propagation velocity, it can accelerate the dissipation of radicals and heat in the end gas, which significantly influences knocking intensity. Moreover, it is found that the effect of turbulence is more pronounced than that of flame propagation velocity in inhibiting knocking. It can be concluded that the intensity of the pressure oscillation depends on the unburned mixture mass as well as the local thermodynamic state induced by flame propagation and turbulence, with mutual interactions. The present work is expected to provide valuable perspective for inhibiting super-knocking of an SI gasoline engine.

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Section: Of 23mentioning

confidence: 99%

Effects of Flame Propagation Velocity and Turbulence Intensity on End-Gas Auto-Ignition in a Spark Ignition Gasoline Engine

et al. 2020

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“…This mean an important reduction of exhaust pollutants (HC, CO, NOx) with special attention in the last few years to particulate emission [3]. Direct injection (DI) has advantages over the port-fuel injected (PFI) engines, such as high precision in fuel metering [4], greater flexibility for different operation regimes, low pumping losses and significant potential in fuel economy benefits [5].…”

Section: Introductionmentioning

confidence: 99%

Flame Front and Burned Gas Characteristics for Different Split Injection Ratios and Phasing in an Optical GDI Engine

2019

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Direct-injection in spark-ignition engines has long been recognized as a valid option for improving fuel economy, reducing CO2 emissions and avoiding knock occurrence due to higher flexibility in control strategies. However, problems associated with mixture formation are responsible for soot emissions, one of the most limiting factors of this technology. Therefore, the combustion process and soot formation were investigated with different injection strategies on a gasoline direct injection (GDI) engine. The experimental analysis was realized on an optically accessible single cylinder engine when applying single, double and triple injection strategies. Moreover, the effect of fuel delivery phasing was also scrutinized by changing the start of the injection during late intake- and early compression-strokes. The duration of injection was split in different percentages between two or three pulses, so as to obtain close to stoichiometric operation in all conditions. The engine was operated at fixed rotational speed and spark timing, with wide-open throttle. Optical diagnostics based on cycle resolved digital imaging was applied during the early and late stages of the combustion process. Detailed information on the flame front morphology and soot formation were obtained. The optical data were correlated to in-cylinder pressure traces and exhaust gas emission measurements. The results suggest that the split injection of the fuel has advantages in terms of reduction of soot formation and NOx emissions and a similar combustion performance with respect to the single injection timing. Moreover, an early injection resulted in higher rates of heat release and in-cylinder pressure, together with a reduction of soot formation and flame distortion. The double injection strategy with higher percentage of fuel injected in the first pulse and early second injection pulse showed the best results in terms of combustion evolution and pollutant emissions. For the operative condition studied, a higher time for mixture homogenization and split of fuel injected in the intake stroke shows the best results.

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“…According to the EU Parliament, by 2020 the EU average passenger car should have a fuel consumption of 3.8 l/100 km, or 95 gCO 2 /km, with gasoline [2]. Such limit may be hard to achieve even with over-expanded downsized engines [3], so powertrain hybridisation and lean combustion concepts are possible options. Lean-burn combustion, either through conventional direct injection [4] or pre-chambers [5], has the potential to improve fuel consumption in spark ignition (SI) engines over conventional homogeneous stoichiometric charging [6].…”

Section: Introductionmentioning

confidence: 99%

“…While battery electric vehicles (BEV) still face a trade-off between energy storage cost and vehicle range, in plug-in hybrid electric vehicles (PHEV) the limitation of battery energy density (1.2 MJ/dm 3 [9] vs. 32 MJ/dm 3 of gasoline) is mended by the adoption of a combustion engine to improve vehicle autonomy [10]. In such particular powertrain architecture, the two-stroke cycle engine has been quoted candidate due to its higher power density, reduced weight and compactness compared to four-stroke engines [11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of the air–fuel charging process in a four-valve supercharged two-stroke cycle GDI engine

Nora

Martins

Machado

et al. 2019

J Braz. Soc. Mech. Sci. Eng.

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Fuel consumption standards imposed in several countries for the next years have prompted the development of hybrid passenger cars with ever smaller internal combustion engines. In such powertrain, fuel consumption is as important as engine packaging and power density, so two-stroke engines may be an option due to their higher combustion frequency compared to four-stroke engines. Therefore, the present research investigates the air-fuel charging process of an overhead four-valve direct injection supercharged engine operating in the two-stroke cycle. The optimum start of fuel injection was evaluated for commercial gasoline by means of indicated and combustion efficiencies where a trade-off was found between early and late fuel injections. By advancing the injection timing, more fuel was prone to short circuit to the exhaust during the valve overlap, while late injections resulted in poor charge preparation. The gas exchange parameters, i.e. charging and trapping efficiencies, were obtained from seventy operating points running at fuel-rich conditions. The Benson-Brandham mixing-displacement scavenging model was then fit to the experimental data with a coefficient of determination better than 0.95. With such model, the air trapping and charging efficiencies could be estimated solely based on the scavenge ratio and exhaust lambda, regardless of the engine load, speed, or air/fuel ratio employed. Further twenty-five different lean-burn testing points were tested to certify the proposed methodology applied to the poppet valve two-stroke engine. The in-cylinder lambda was calculated and found different from the exhaust lambda due to mixing between burned gases and intake air during the scavenging process.

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Effects of applying a Miller cycle with split injection on engine performance and knock resistance in a downsized gasoline engine

Cited by 74 publications

References 26 publications

Effects of Flame Propagation Velocity and Turbulence Intensity on End-Gas Auto-Ignition in a Spark Ignition Gasoline Engine

Effects of Flame Propagation Velocity and Turbulence Intensity on End-Gas Auto-Ignition in a Spark Ignition Gasoline Engine

Flame Front and Burned Gas Characteristics for Different Split Injection Ratios and Phasing in an Optical GDI Engine

Experimental investigation of the air–fuel charging process in a four-valve supercharged two-stroke cycle GDI engine

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