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The traditional thermal environment management of the passenger compartment adopts the unified regulation method. Air distribution formed in this manner often causes thermal comfort and energy consumption problems. In view of the problems of conventional airflow organization, a new air supply strategy-variable air volume and temperature strategy is proposed. In this air supply strategy, variable air volume and variable temperature air supply is carried out according to the characteristics of thermal comfort requirements of passengers in different periods and positions in the cabin. STAR-CCM + software coupled with THESUES-FE software was implemented and compared with different air supply methods. The performance of the air supply strategy was evaluated based on PMV-PPD evaluation index. The results show that the variable air volume variable temperature air supply strategy has certain advantages and improves the thermal comfort level of the crew cabin. The cooling capacity of the automobile air conditioning is allocated effectively, thus improving the satisfaction of the occupants to the thermal environment. This strategy not only saves energy, but also improves the cooling effect in the cabin. [ABSTRACT FROM AUTHOR]

Linear hydrogen engine is a new type of energy conversion device to supports variable compression ratio operation for clean emission. However, the new hydrogen engine using conventional spark ignition shows slow combustion speed and low thermal efficiency. This study makes a preliminary assessment to discuss the application of diesel pilot-ignition technology in linear hydrogen engine aiming to accelerate combustion and improve efficiency. A new coupling model between dynamics and thermodynamics is proposed and then iteratively calculated to give insight the interrelationship of combustion and motion in a diesel pilot-ignited linear hydrogen engine, while the effect of injection position on the hydrogen engine combustion is also investigated to make clear the feasibility of combustion optimization. The results indicate that the linear hydrogen engine is speeded by properly advancing the injection to promote combustion, and it has a positive effect on in-cylinder gas temperature, pressure and pressure rise rate, unless the injection is too early which results in higher NO emissions and aggravate the working intensity of the engine. In addition, the closer the fuel injection is to the top dead center, the incomplete combustion of hydrogen and diesel in the cylinder, the decrease of engine fuel economy and the increase of soot emissions. There is an optimal thermal efficiency of 40.7% for the LHE when it operates in the 0.8 mm injection position condition. [Display omitted] • The application of diesel pilot-ignition technology in linear hydrogen engine is discussed. • A new coupling simulation of dynamic and thermodynamics is presented. • The hydrogen engine is speeded by properly advancing the injection for combustion. • The closer the injection is to top dead center, the incomplete combustion and the more soot. [ABSTRACT FROM AUTHOR]

As a clean and sustainable energy source, hydrogen is widely considered as an engine fuel by top researchers. In view of the fact that the uneven fuel mixture of diesel fuel deteriorated the combustion and emissions process, it is expected to adopt diesel and hydrogen dual-fuel combustion technology to optimize combustion and heat release of diesel engine. In this study, experiments are carried out on a diesel engine and the combustion characteristics of the engine with different hydrogen ratios (RH) are compared. It has been found that hydrogen addition is conducive to accelerate the heat release rate and improve the thermal efficiency. Specifically, compared with pure diesel conditions, the peak pressure increased by 7.7% and the cumulative heat release rate increased by 3.7% under the condition of RH of 20%. Moreover, although the effect on the ignition delay period is not clear, the higher RH brings about earlier heat release center and more cumulative heat release while enhancing the heat release of premixed combustion reducing the diffusion combustion and post-combustion. [ABSTRACT FROM AUTHOR]

Purpose A free-piston engine (FPE) is an unconventional engine that abandons the crank system. This paper aims to focus on a numerical simulation for the lubricating characteristics of piston rings in a single-piston hydraulic free-piston engine (HFPE).Design/methodology/approach A time-based numerical simulation program was built using Matlab to define the piston motion of the new engine. And a lubrication mode of piston rings was built which is based on the gas flow equation, hydrodynamic lubrication equation and the asperity contact equation. The piston motion and the lubrication model are coupled, and then the finite difference method is used to obtain the piston rings lubrication performances of the FPE. Meanwhile, the lubrication characteristics of the new engine were compared with those of a corresponding conventional crankshaft-driven engine.Findings The study results indicate that compared with the traditional engine, the expansion stroke of the HFPE is longer, and the compression stroke is shorter. Lubrication oil film of the new engine is thicker than the traditional engine during the initial stage of compression stroke and the final stage of the power stroke. The average friction force and power of the hydraulic free piston engine are slightly lower than those of the traditional engine, but the peak friction power of the FPE is significantly greater than that of the traditional engine. With an increase in load, the friction loss power and friction loss efficiency decrease, and with a decrease in equivalence ratio, the friction power loss reduces, but the friction loss efficiency decreases first and then increases.Research limitations/implications In this paper, only qualitative analysis was performed on the tribological difference between conventional crankshaft engine and HFPE, instead of a quantitative one.Practical implications This paper contributes to the tribological design method of HFPE.Social implications No social implications are available now, as the HFPE is under the development phase. However, the authors are positive that their work will be commercialized in the near future.Originality/value The main originality of the paper can be introduced as follows: the lubrication and friction characteristics of the new engine (HFPE) were investigated and revealed, which have not been studied before; the effect of the HFPE’s special piston motion on the tribological characteristics was considered in the lubrication simulation. The results show that compared with the traditional crankshaft engine, the new engine shows a different lubrication performance because of its free piston motion. [ABSTRACT FROM AUTHOR]

A low-cycle thermal fatigue test at heat shock is carried out on a simple specimen of cast iron, as the material of cylinder head. Meanwhile a finite element (FE) model for specimen is built and a FE simulation on the temperature, stress and strain fields of specimen is conducted with the fatigue life of the specimen predicted. The fatigue life predicted well agrees with test result, indicating the correctness of the model built and the simulation scheme used. The low-cycle thermal fatigue damage of cylinder head has a certain similarity to that of cast iron specimen, so the test and simulation methods used in the paper are also suitable for the study on the thermal fatigue life of real cylinder head. [ABSTRACT FROM AUTHOR]

In this paper, vortex characteristics and velocity distribution in the chamber region were studied by numerical method. The three-dimensional moving grid and Improved Delayed Detached Eddy Simulation Shear-Stress Transport model which is a hybrid RANS/LES model were used to predict evolution processes of streamlines and velocity change in small rotary engine. The simulation results show that vortex has always existed in intake process and has gone through three stages, including generation, brakedown, regeneration. The generation is mainly due to intake charge. The brakedown and regeneration is because of the shear and friction of the rotor face. Vortex radius in the leading gradually increases and in the trailing decreases in intake stroke from 490 °C BTDC to 390 °C BTDC. And the position of vortex core in the leading has no obvious change and in the trailing moves towards the trailing apex along the rotor wall. In the intake process, the airflow velocity in the middle of chamber is much higher than the one at both sides, even up to hundreds of times. In the compression process, the large velocity gradient in the trailing and high variation frequency in the leading are due to the shear and friction of the rotor face. • IDDES-SST method was used to calculate the flow field in small rotary engine. • The mechanism of vortex generation was investigated in combustion chamber. • The evolution process of vortex at different cross section was studied. • The velocity distribution and change at different cross section was analyzed. [ABSTRACT FROM AUTHOR]

The temperature rise characteristics of PMSM (permanent magnet synchronous motor) during operation were studied under the condition of BHT (boiling heat transfer) in cooling water. The subcooling boiling heat transfer model, RPI (Rensselaer polytechnic institute), was used to calculate and improve the computational accuracy of simulation results. The experiments have shown that, when the motor was tested and simulated after preheating, the temperature rise characteristics were similar to test data because the boiling heat transfer phenomenon of the motor was taken into account, with an error of 1.7%, which was more accurate than the error of 7.5% without boiling. Therefore, from the results obtained from the experiments, the phenomenon of boiling heat transfer in cooling system has a significant effect on the temperature rise characteristic of the motor, which should be regarded as an important factor. Due to the influence of two-phase flow boiling heat transfer, the temperature rise of the motor in the plain areas is 4–5 °C higher than that in the high altitude areas. Consequently, if the motor is operated in high altitude areas, its temperature rise characteristic has better effect compared with plain area. Additionally, when BHT in cooling water is considered, the temperature of the motor drops as the rate of flow increases. In the meantime, the temperature difference between the minimum flow rate and the maximum flow rate is about 1 °C, which means that the increase in rate of flow can enhance the boiling heat transfer effect. [ABSTRACT FROM AUTHOR]

To research the quality of the hydrogen–air mixture formation and the combustion characteristics of the hydrogen fueled engine under different hydrogen injection timings, nozzle hole positions and nozzle hole diameter, a three-dimensional simulation model for a PFI hydrogen internal combustion engine with the inlet, outlet, valves and cylinder was established using AVL Fire software. In the maximum torque condition, research focused on the variation law of the total hydrogen mass in the cylinder and inlet and the space distribution characteristics and variation law of velocity field, concentration field and turbulent kinetic energy under different hydrogen injection parameters (injection timings, nozzle hole positions and nozzle hole area) in order to reveal the influence of these parameters on hydrogen–air mixture formation process. Then the formation quality of hydrogen–air mixture was comprehensively evaluated according to the mixture uniformity coefficient, the remnant hydrogen percentage in the inlet and restraining abnormal combustion (such as preignition and backfire). The results showed that the three hydrogen injection parameters have important influence on the forming quality of hydrogen–air mixture and combustion state. The reasonable choice of the nozzle hole position of hydrogen, nozzle hole diameter and the hydrogen injection time can improve the uniformity of the hydrogen–air mixing in the cylinder of the hydrogen internal combustion engine, and the combustion heat release reaction is more reasonable. At the end of the compression stroke, the equivalence ratio uniform coefficient increased at first and then decreased with the beginning of the hydrogen injection. When hydrogen injection starting point was with 410–430°CA, equivalence ratio uniform coefficient was larger, and ignition delay period was shorter so that the combustion performance index was also good. And remnant hydrogen percentage in the inlet was less, high concentration of mixed gas in the vicinity of the inlet valve also gathered less, thus suppressing the preignition and backfire. With the increase of the distance between the nozzle and the inlet valve, the selection of the hydrogen injection period is narrowed, and the optimum hydrogen injection time was also ahead of time. The results also showed that it was favorable for the formation of uniform mixing gas when the nozzle hole diameter was 4 mm. [ABSTRACT FROM AUTHOR]