Influence of nozzle hole diameter and orifice diameter on dme spray to get the similar heat value with diesel spray using the constant volume chamber

Low heating value (LHV) of di-methyl ether (DME) is lower than that of diesel. To get the similar heat value with diesel from the diesel engine operation, single injection quantity of DME should be increased. This investigation was tried to increase the injection quantity of DME by the modified diesel injector and investigated the penetration length and spray angle of DME spray. DME was injected by using three-type modified diesel injectors those nozzle-hole diameters (Injector 1: 1.66 mm, Injector 2 and 3: 0.25 mm) and orifice diameters were different (Injector 1 and 2: 0.6 mm, Injector 3: 1 mm). Spray characteristics of DME was investigated with a various ambient pressures (2.5, 5.0 MPa) in the constant volume chamber and a fuel was injected by varied injection pressure from 35 to 70 MPa by interval of 5 MPa using a DME common rail fuel injection system. The result shows that DME injection quantity by Injector 3 was 1.69 ~ 2.02 times larger than that of diesel injection quantity by Injector 1. In this case, DME spray got the similar heat value compared with diesel spray. The penetration speed of DME spray by Injector 3 was the fastest, thus when the spray development was end, the penetration length of DME spray by Injector 3 was the longest compared with the other cases. In case of the spray angle, Injector 2 and 3 had the similar spray angle and these were larger than that of diesel and DME sprays by Injector 1. As the result, Injector 3 was the solution for how to solve the low heating value of DME.     

New evidence on walking distances to transit stops: identifying redundancies and gaps using variable service areas

The percentage of the population being served by a transit system in a metropolitan region is a key system performance measure but depends heavily on the definition of service area. Observing existing service areas can help identify transit system gaps and redundancies. In the public transit industry, buffers at 400 m (0.25 miles) around bus stops and 800 m (0.5 miles) around rail stations are commonly used to identify the area from which most transit users will access the system by foot. This study uses detailed OD survey information to generate service areas that define walking catchment areas around transit services in Montreal, Canada. The 85th percentile walking distance to bus transit service is found to be around 524 m for home-based trip origins, 1,259 m for home-based commuter rail trip origins. Yet these values are found to vary based on our analysis using two statistical models. Walking distances vary based on route and trip qualities (such as type of transit service, transfers and wait time), as well as personal, household, and neighbourhood characteristics. Accordingly, service areas around transit stations should vary based on the service offered and attributes of the people and places served. The generated service areas derived from the generalized statistical model are then used to identify gaps and redundancies at the system and route level using Montreal region as an example. This study can be of benefit to transport engineers and planners trying to maximize transit service coverage in a region while avoiding oversupply of service.     

Optimal design of the exhaust system layout to suppress the discharge noise from an idling engine

At the idle engine speed, the exhaust discharge noise is influenced by resonances in the whole system, which is composed of connecting pipes and silencers. This pipe resonance radiates a high level of low frequency discharge noise, which is dominated by the low order harmonics of the engine firing frequency. This low frequency noise deteriorates the vehicle’s interior noise level and quality. The following study attempted to optimize the layout of an exhaust system to minimize low frequency noise by changing the position of silencers and the lengths of inlet and outlet pipes in each silencer. After modeling the exhaust system using four-pole parameters, the acoustical performance of the system was evaluated using the system insertion loss. In the optimization, the virtual attenuation coefficient, which corresponds to the amount of attenuation coefficient required for the silencers, was calculated to find a minimum value for the layout. The simulated annealing method, which is also known as finding an optimal, was employed in searching for the optimized exhaust layout. Test examples of two cases, for two and six design variables, were used. When the number of design variables was two, the positions of the center and rear silencers were considered. When the number of design variables was six, the positions of the two silencers and the lengths of the inlet and outlet pipes were considered. Three typical layouts for the exhaust system of each case were designed, including the given system and an optimal system. By comparing the predicted and measured discharge noise level, it was confirmed that the optimized exhaust layout has a higher noise reduction than the other layout designs.     

Nonlinear pricing on private roads with congestion and toll collection costs

Nonlinear pricing (a form of second-degree price discrimination) is widely used in transportation and other industries but it has been largely overlooked in the road-pricing literature. This paper explores the incentives for a profit-maximizing toll-road operator to adopt some simple nonlinear pricing schemes when there is congestion and collecting tolls is costly. Users are assumed to differ in their demands to use the road. Regardless of the severity of congestion, an access fee is always profitable to implement either as part of a two-part tariff or as an alternative to paying a toll. Use of access fees for profit maximization can increase or decrease welfare relative to usage-only pricing for profit maximization. Hence a ban on access fees could reduce welfare.     

Automotive windshield — pedestrian head impact: Energy absorption capability of interlayer material

During accident, the interlayer of windshield plays an important role in the crash safety of automotive and protection of pedestrian or passenger. The understanding of its energy absorption capability is of fundamental importance. Conventional interlayer material of automotive windshield is made by Polyvinyl butyral (PVB). Recently, a new candidate of high-performance nanoporous energy absorption system (NEAS) has been suggested as a candidate for crashworthiness. For the model problem of pedestrian head impact with windshield, we compare the energy absorption capabilities of PVB and NEAS interlayers, in terms of the contact force, acceleration, velocity, head injury criteria, and energy absorption ratio, among which results obtained from PVB interlayers are validated by literature references. The impact speed is obtained from virtual test field in PC-CRASH, and the impact simulations are carried out using explicit finite element simulations. Both the accident speed and interlayer thickness are varied to explore their effects. The explicit relationships established among the energy absorption capabilities, impact speed, and interlayer material/thickness, are useful for safety evaluation as well as automotive design. It is shown that the NEAS interlayer may absorb more energy than PVB interlayer and it may be a competitive candidate for windshield interlayer.     

「台湾桃园国际机场联外捷运系统建设计划」地下工程的设计与施工

介绍「台湾桃园国际机场联外捷运系统建设计划」中机场区段地下工程的设计成果,并探讨施工时将面临的主要工程问题如,潜盾隧道穿越营运中的机场滑行道下方需考虑对其进行保护、隧道遭遇既有地锚的处理方式,及明挖覆盖隧道或车站于卵砾石层进行开挖,临时挡土措施及潜盾隧道的掘进作业,需考虑卵砾石大粒径与高硬度的特性等等设计考虑.现有数据显示,透过适当的机具改良、辅助工法的应用及良好的施工管理,即使是在高地下水压的卵砾石层,施作地下连续壁及以潜盾机施作隧道并无太大困难,且施工引致的地表沉陷及施工精度亦可获得良好的控制.     

Modeling and model predictive control for hybrid electric vehicles

This paper builds up a typical model of a parallel hybrid electric vehicle and develops model predictive controllers for this model to control the speeds and torques for fast clutch engagement with high driving comfort and low jerk. Some modified algorithms for model predictive controllers are studied to improve their ability to track the desired speed setpoints, subject to input and output constraints.     

Majorization of working parameters for non-thermal plasma reactor and impact on no oxidation of diesel engine

The main target of this work is to realize the function of pre-oxidizing NO from diesel engine’s exhaust by using self-designed double-dielectric Non-thermal Plasma (NTP) reactor. The majorized discharge frequency and discharge peak to peak voltage (V_p-p) range for NTP reactor were obtained through air discharge test. The diesel engine test bench was established to observe the effect of NTP on the volume fraction of NO. The results showed that there were more active substances and fewer by-products in NTP reactor when discharge frequency was 9 kHz and V_p-p was between 9 kV and 23 kV; Exhaust flows had insignificant effect on the performance of NTP pre-oxidizing NO; The ability of NTP to pre-oxidize NO gradually weakened with the increase of engine load, and when the engine load were 0 % and 25 %, the ratio of NO/NO₂ could reach 1. In such working conditions, SCR system could improve the conversion rate of the NO_x at low-temperature zone through quick reaction combined with NTP.     

Combined effect of boost pressure and injection timing on the performance and combustion of CNG in a DI spark ignition engine

There is an increasing interest in supercharging spark ignition engines operating on CNG (compressed natural gas) mainly due to its superior knock resisting properties. However, there is a penalty in volumetric efficiency when directly injecting the gaseous fuel at early and partial injection timings. The present work reports the combined effects of a small boost pressure and injection timing on performance and combustion of CNG fueled DI (direct injection) engine. The experimental tests were carried out on a 4-stroke DI spark ignition engine with a compression ratio of 14. Early injection timing, when inlet valves are still open (at 300°BTDC), and partial injection timing, in which part of the injection occurs after the inlet valves are closed (at 180°BTDC), were varied at each operating speed with variation of the boost pressure from 2.5 to 10 kPa. A narrow angle injector (NAI) was used to increase the mixing rate at engine speeds between 2000 and 5000 rpm. Similar experiments were conducted on a naturally aspirated engine and the results were then compared with that of the boosting system to examine the combined effects of boost pressure and injection timing. It was observed that boost pressure above 7.5 kPa resulted in an improvement of performance and combustion of CNG DI engine at all operating speeds. This was manifested in the faster heat release rates and mass fraction burned that in turn improved combustion efficiency of the boosting system. An increased in cylinder pressure and temperature was also observed with boost pressure compared to naturally aspirated engine. Moreover, the combustion duration was reduced due to concentration of the heat release near to the top dead center as the result of the boost pressure. Supercharging was also found to reduce the penalty of volumetric efficiency at both the simulated port and partial injection timings.     

Brushless PM machine drive in electric and hybrid electric vehicles based on the space vector current control

This paper presents a space vector current controller for a brushless permanent magnet motor in electric and hybrid electric vehicles. The proposed current controller selects space vectors based on the sector selection under a three-level hysteresis comparator to decrease the current ripple. The proposed approach can improve the performance of a brushless PM drive such as the average switching frequency and the total harmonic distortion (THD) compared with the conventional hysteresis current control. The experiment is performed first to verify the proposed control. Then, the method is implemented in a hybrid electric vehicle simulation model with standard driving cycles based on the control strategy to evaluate the drive performance in the vehicle system. The experimental and simulation results indicate that the presented control can improve the performance of the brushless PM machine drive.