Search Results

Hybrid powertrain has been proven to be an effective fuel-saving technology in commercial vehicles, but many hybrid commercial vehicles still use conventional diesel engines, resulting in limited fuel savings. The main purpose of this study is to enhance the thermal efficiency of a dedicated hybrid diesel engine focusing on the characteristic operating conditions. Via fundamental thermodynamics process analysis of internal combustion engine, steel piston with high compression ratio, air system involving two-stage turbocharger(2TC) with an intercooler, and late intake valve closing(IVC) timing are proposed to improve the thermal efficiency of the engine. Experimental results show that high compression ratio and lower thermal conductivity of the combustion chamber surface lead to lower heat release rates, requiring optimization of piston profile to accelerate the mixing rate. Besides, high compression ratio also leads to higher mechanical losses.

Focusing on the dual-mode dual-fuel (DMDF) combustion concept, a combined optimization of the piston bowl geometry with the fuel injection strategy was conducted at low, mid, and high loads. By coupling the KIVA-3V code with the enhanced genetic algorithm (GA), a total of 14 parameters including the piston bowl geometric parameters and the injection parameters were optimized with the objective of meeting Euro VI regulations while improving the fuel efficiency. The optimal piston bowl shape coupled with the corresponding injection strategy was summarized and integrated at various loads. Furthermore, the effects of the key geometric parameters were investigated in terms of organizing the in-cylinder flow, influencing the energy distribution, and affecting the emissions. The results indicate that the behavior of the DMDF combustion mode is further enhanced in the aspects of improving the fuel economy and controlling the emissions after the bowl geometry optimization.

This article first analyzes the driving characteristics of vehicles in Intelligent Vehicle Infrastructure Cooperative Systems, summarizing and proposing four characteristics, including a wider field of view, easier lane-changing conditions, less speed loss, and more flexible cooperation among vehicles than in the traditional lane-changing situation. Analysis and comparison of the update sequence in cellular automata based on the four characteristics, namely, synchronous update and asynchronous update, longitudinal vehicle sequence update and random update, horizontal express vehicle priority, and random priority. Three kinds of cooperative lane changes unique to the vehicle-road collaborative environment were discovered, which are dangerous lane change, slow car giving way, and space redistribution. The three kinds of coordinated lane change were simulated and compared with the basic diagram of the improved model and the traditional model.

This work numerically investigates the detailed combustion kinetics of partially premixed combustion (PPC) in a diesel engine under three different premixed ratio fuel conditions. A reduced Primary Reference Fuel (PRF) chemical kinetics mechanism was coupled with CONVERGE-SAGE CFD model to predict PPC combustion under various operating conditions. The experimental results showed that the increase of premixed ratio (PR) fuel resulted in advanced combustion phasing. To provide insight into the effects of PR on ignition delay time and key reaction pathways, a post-process tool was used. The ignition delay time is related to the formation of hydroxyl (OH). Thus, the validated Converge CFD code with the PRF chemistry and the post-process tool was applied to investigate how PR change the formation of OH during the low-to high-temperature reaction transition. The reaction pathway analyses of the formations of OH before ignition time were investigated.

Primary breakup of a liquid jet is a process of enormous complexity, involving interfacial dynamics, topology changes, and turbulence. In macro-scale simulations for practical problems, the primary breakup is usually too expensive to be fully resolved and thus is typically represented by phenomenological models. The recent advancement of numerical methods and computer power enables large-scale high-fidelity simulations of primary breakup. The high-level details provided by simulation can be used to verify the assumptions made in existing models and also to develop new models through both physics- or data-based approaches. The present paper will present the state-of-the-art high-fidelity simulation of the primary breakup of a gasoline surrogate jet. The simulation parameters were chosen following the Engine Combustion Network (ECN) ``Spray G" conditions and thus are similar to realistic engine conditions.

The non-conventional diesel nozzles have attracted more and more attention for their ability to promote jet breakup. In the present study, the internal nozzle flow and jet breakup relying on the convergent-divergent nozzle are investigated by combining the cavitation model and LES model with Multi-Fluid-Quasi-VOF model based on the OpenFOAM code. This is a novel method for which the interphase forces caused by the relative velocity of gas and liquid can be taken into account while sharpening the gas-liquid interface, which is able to accurately present the evolution processes of cavitation and jet breakup. Primarily, the numerical model was verified by the mass flow rate, spray momentum flux, discharge coefficient and effective jet velocity of the prototype Spray D nozzle from the literature.

OH, soot and temperature distributions of wall-impinging diesel fuel spray were investigated in a high-temperature high-pressure constant volume combustion vessel. The ambient temperature (Ta) was set as 773 K, and the wall temperature (Tw) was set as 523 K, 673 K, 773 K, respectively. Three different injection pressures (Pi) of 60 MPa, 100 MPa, 160 MPa, and the ambient pressures (Pa) of 4 MPa were applied. The OH spatial distributions of wall-impinging spray were measured by the method of OH chemiluminescence imaging. Two-color pyrometry was applied to evaluate the spatial distributions of KL factor and flame temperature of wall-impinging spray. The results reveal that, OH chemiluminescence is observed in the region near the impingement point firstly. The regions of high OH chemiluminescence intensity and high KL factor appear in the location near the wall surface along the whole combustion process.

Although turbulence plays a critical role in engines operated within low temperature combustion (LTC) regime, its interaction with chemistry on auto-ignition at low-ambient-temperature and lean-oxygen conditions remains inadequately understood. Therefore, it is worthwhile taking turbulence-chemistry interaction (TCI) into consideration in LTC engine simulation by employing advanced combustion models. In the present study, large eddy simulation (LES) coupled with linear eddy model (LEM) is performed to simulate the ignition process in n-heptane spray under engine-relevant conditions, known as Spray H. With LES, more details about unsteady spray flame could be captured compared to Reynolds-averaged Navier-Stokes equations (RANS). With LEM approach, both scalar fluctuation and turbulent mixing on sub-grid level are captured, accounting for the TCI. A skeletal mechanism is adopted in this numerical simulation, including 41 species and 124 reactions.

Syngas is considered to be a promising alternative fuel for the dual-fuel reactivity controlled compression ignition (RCCI) engine to reduce the fuel consumption and emissions. However, the optimal syngas compositions and fuel supply strategies in RCCI combustion are significantly affected by engine configurations, which have not been investigated yet. In this study, by integrating the KIVA-3V code and the non-dominated sort genetic algorithm II (NSGA-II), the optimizations for a 0.477 L single-cylinder engine with shallow/wide piston bowl (Engine A) and a 1.325 L single-cylinder engine with conventional omega-type piston (Engine B) under the syngas/diesel RCCI combustion were performed. The optimized operating parameters include the fuel-supply strategies, syngas compositions, and intake conditions. The results indicate that the fuel-supply strategy is flexible in Engine A due to the shallow/wide piston bowl and the relatively small cylinder bore.

Liquefied natural gas (LNG) engine could provide both reduced operating cost and reduction of greenhouse gas (GHG) emissions. Stoichiometric operation with EGR and the three-way catalyst has become a potential approach for commercial LNG engines to meet the Euro VI emissions legislation. In the current study, numerical investigations on the knocking tendency of several combustion chambers with different geometries and corresponding performances were conducted using CONVERGE CFD code with G-equation flame propagation model coupled with a reduced natural gas chemical kinetic mechanism. The results showed that the CFD modeling approach could predict the knock phenomenon in LNG engines reasonably well under different thermodynamic and flow field conditions.

The potential of diesel/gasoline RCCI combustion coupled with late intake valve closing (LIVC) and double direct injection of diesel for meeting high fuel efficiency with ultra-low emissions was investigated in this study. The study was aiming at high load operation in a heavy-duty diesel engine. Based on the reactivity stratification of RCCI combustion, the employment of double injection of diesel fuel provided concentration stratification of the high-reactivity fuel, which is to further realize effective control of the combustion process. Meanwhile, late intake valve closing (LIVC) strategy is introduced to control the maximum in-cylinder pressure and nitrogen oxides (NOx) emissions.

The application of oxygen-enriched or oxy-fuel combustion coupled with carbon capture and storage technology has zero carbon dioxide emission potential in the boiler and gas turbine of the power plant. However, the oxygen-enriched combustion with high oxygen level has few studies in internal combustion engines. The fundamental issues and challenges of high oxygen level are the great differences in the physical properties and chemical effects compared with the combustion in air condition. As a consequence, the diesel spray combustion characteristics at high oxygen level were investigated in an optical constant volume vessel. The oxygen volume fraction of tested gas was from 21% to 70%, buffered with argon. The high-speed color camera was used to record the natural flame luminosity.

In order to achieve high-efficiency and clean combustion in HCCI engines, combustion must be controlled reasonably. A great variety of species with various reactivities can be produced through low temperature oxidation of fuels, which offers possible solutions to the problem of controlling in-cylinder mixture reactivity to accommodate changes in the operating conditions. In this work, in-cylinder combustion characteristics with low temperature reforming (LTR) were investigated in an optical engine fueled with low octane number fuel. LTR was achieved through low temperature oxidation of fuels in a reformer (flow reactor), and then LTR products (oxidation products) were fed into the engine to alter the charge reactivity. Primary Reference Fuels (blended fuel of n-heptane and iso-octane, PRFs) are often used to investigate the effects of octane number on combustion characteristics in engines.

Dimethyl ether (DME) attracts increasing attentions in recent years, because it can reduce the carbon monoxide (CO), unburned hydrocarbon (HC), and soot emissions for engines as the transportation fuel or the fuel additive. In this paper, a reduced DME oxidation mechanism is developed using the decoupling methodology. The rate constants of the fuel-related reactions are optimized using the non-dominated sorting genetic algorithm II (NSGA-II) to reproduce the ignition delay times in shock tubes and major species concentrations in jet-stirred reactors (JSR) over low-to-high temperatures. In NSGA-II, the range of the rate constants was considered to ensure the reliability of the optimized mechanism. Moreover, an improved objective function was proposed to maintain the faithfulness of the optimized mechanism to the original reaction mechanism, and a new method was presented to determine the optimal solution from the Pareto front.

Gasoline partially premixed combustion shows the potential to achieve clean and high-efficiency combustion. Injection strategies show great influence on in-cylinder air flow and in-cylinder fuel distribution before auto-ignition, which can significantly affect the combustion characteristics and emissions. This study explored the effects of various injection strategies, including port fuel injection (PFI), single direct injection (DIm), double direct injection (DIp+DIm) and port fuel injection coupled with a direct injection (PFI+DIm) on the combustion characteristics and emissions in a modified single cylinder heavy-duty diesel engine fueled with 92# gasoline at low load. The investigation consists of two parts. Firstly, the comparison among PFI, PFI+DIm, and DIp+DIm strategies was conducted at a fixed CA50 to explore the effects of PFI+DIm and DIp+DIm strategies on the thermal efficiency and combustion stability.

The flame structure and combustion characteristics of wall-impinging diesel fuel spray were investigated in a high-temperature high-pressure constant volume combustion vessel. The ambient temperature (Ta) was set to 773 K. The wall temperatures (Tw) were set to 523 K, 673 K and 773 K respectively. Three different injection pressures (Pi) of 600 bar, 1000bar and 1600bar, two ambient pressures (Pa) of 2 MPa and 4 MPa were applied. The flame development process of wall-impinging spray was measured by high-speed photography, which was utilized to quantify the flame luminosity intensity, ignition delay and flame geometrical parameters. The results reveal that, as the wall temperature increases, the flame luminosity intensity increases and the ignition delay decreases.

The dual-fuel Reactivity Controlled Compression Ignition (RCCI) combustion could achieve high efficiency and low emissions over a wide range of operating conditions. However, further high load extension is limited by the excessive pressure rise rate and soot emission. Polyoxymethylene dimethyl ethers (PODE), a novel diesel alternative fuel, has the capability to achieve stoichiometric smoke-free RCCI combustion due to its high oxygen content and unique molecule structure. In this study, experimental investigations on high load extension of gasoline/PODE RCCI operation were conducted using late intake valve closing (LIVC) strategy and intake boosting in a single-cylinder, heavy-duty diesel engine. The experimental results show that the upper load can be effectively extended through boosting and LIVC with gasoline/PODE stoichiometric operation.

Flash boiling spray is effective in improving the atomization and evaporation characteristics for gasoline direct injection engines. However, for a multi-hole injector the morphology structure of spray has an obvious change with the fuel temperature increasing or the ambient pressure decreasing, which influences the process of mixture formation and flame propagation. Specially, the spray collapses with both long penetration and a narrow spray angle above certain high superheat degree, which deteriorates air/fuel mixing and hence increases emissions. It is not desired for engine applications while the mechanism of spray structure transformation for multi-hole injector still remains unclear. In the present study, a systematic flash boiling spray model for multi-hole injector is built to investigate the flash boiling spray of multi-hole injector.

ADAMS, SIMULINK, and ADAMS-SIMULINK co-simulation models of component test systems, Multi-Axis-Simulation-Table (MAST) systems, and spindle-coupled vehicle testing system (MTS 329) were created. In the ADAMS models, the mechanical parts, joints, and bushings were modeled. Hydraulic and control elements were absent. The SIMULINK models modeled control and hydraulic elements including actuator dynamics, servo valve dynamics, closed loop control, three-variable control, matrix control, and coordinate transformation. However, the specimen had to be simplified due to the limitation of SIMULINK software. The ADAMS-SIMULINK co-simulation models considered hydraulic and control components in the SIMULINK portion and mechanical components in ADAMS portion. The interaction between the ADAMS and SIMULINK portions was achieved using ADAMS/Control.

In this work the gasoline compression ignition (GCI) combustion characterized by both premixed gasoline port injection and gasoline direct injection in a single-cylinder diesel engine was investigated experimentally and computationally. In the experiment, the premixed ratio (PR), injection timing and exhaust gas recirculation (EGR) rate were varied with the pressure rise rate below 10 bar/crank angle. The experimental results showed that higher PR and earlier injection timing resulted in advanced combustion phasing and improved thermal efficiency, while the pressure rise rates and NOx emissions increased. Besides, a lowest ISFC of 176 g/kWh (corresponding to IMEP =7.24 bar) was obtained, and the soot emissions could be controlled below 0.6 FSN. Despite that NOx emission was effectively reduced with the increase of EGR, HC and CO emissions were high. However, it showed that GCI combustion of this work was sensitive to EGR, which may restrict its future practical application.