Concerning the influence of air pollution from ship to coastal regions, author reviewed some calculation cases of air pollutant emission from ship, and some results of atmospheric diffusion simulations in Tokyo Bay. Furthermore, it was considered that the environmental risk assessment becomes important matters, and thusly an example of simple risk evaluation of an anchoring ship was examined. Recognition to risk of harmful chemical substances increases, and necessity to carry out environmental risk evaluation from a ship rises. On this account it is necessary to establish the evaluation method to calculate chemical substances emission from ship, and the method of environment impact assessment of coastal area.
Measurements of spray angle, spray penetration, ignition delay, flame extent and flame temperature are made in an optically accessible, electrically heated constant volume chamber of relatively large dimensions. The combustion process of both Marine Diesel Oil (MDO) and a poor quality Heavy Fuel Oil (HFO) are analysed and compared. Soot temperature is measured using the two-colour method. The measured data are compared with predictions using the CFD package StarCD. Fuel evaporation, ignition and combustion models, which are developed specifically for heavy residual fuel oil are applied. Initial spray atomisation is modelled with the blob method as well as with the Max Plank Institute (MPI) model, which creates a denser spray core than the blob atomisation model, as well as child droplets from aerodynamic stripping and collision. The denser core results in increased droplet coalescence during the subsequent secondary breakup phase, resulting in greater droplet persistence and spray penetration during combustion. Droplet persistence and spray penetration are much greater for HFO than MDO. Higher chamber initial temperature significantly reduces ignition delay period and flame lift-off distance. Flame lift-off distance and ignition delay for MDO are less than for HFO. The fuel model proposed here reproduces these trends successfully.
Study of diesel engine emission and fuel economy requires a basic understanding of fuel-air mixture formation processes, which is because of significant dependence of diesel combustion performance on the fuel spray injection into the combustion chamber. This paper reviews recent investigations on diesel spray structure, which include internal flow of the nozzle, the breakup behavior of a liquid jet, spray tip penetration, and drop size distribution. Their corresponding empirical equations are also presented. Based on those equations, a phenomenological simulation model has been developed to predict the combustion performance, thermal efficiency, and diesel emissions.
The present paper is intended to report LES approach of non-evaporative and evaporative diesel sprays in order to describe the heterogeneous structure in the diesel spray. The computational code used in LES approach is KIVALES in which LES is incorporated into conventional KIVA code. In KIVALES, κ-Δ model and gradient diffusion model are employed for the SGS stress model and SGS scalar model, respectively. The atomization is modeled by using modified TAB model, and the calculation method of convective terms for capturing the turbulent vortices uses the Interpolated Donor Cell differencing scheme. Using LES approach, the three-dimensional turbulent vortices can be captured, and the calculation of intermittency at outer edge of the spray in the non-evaporative and evaporative diesel sprays is also derived. Furthermore, good agreements of spray characteristics, such as spray tip penetration, Sauter mean diameter and liquid length, are obtained between LES results and experimental results.
Practical simulations of combustors are successfully conducted by use of the combustion models based on the laminar flamelet concept. On the other hand, thanks to the recent progress of computer performance, simulations with detailed chemistry and rigorous transport properties are becoming practical about simple flame configurations. In the latter simulations, complicated flame structures are reproduced and sometimes they look largely different from laminar flamelets. The authors succeeded in capturing a hydrogen jet lifted flame by a detailed simulation. The flame consisted of three elements, a leading edge flame, outer island-like diffusion flames, and inner turbulent rich premixed flame. Non-flamelet-like structures were observed in the inner vigorously turbulent part of the flame and they are investigated in terms of the balance between the fuel consumption and the fuel molecular diffusion and the dependency of the fuel consumption on the fuel molecular diffusion. The results show the flames cannot be described by the laminar flamelet concept, because the turbulent eddies can penetrate into the flames to modify the internal structure. New analytical concepts are necessary to understand and to model such kind of flames.
The replacement of steam turbine to diesel engine after the oil crisis, has not taken place with regard to LNG carriers and still continuing using steam turbine. However, the alternative ship has appeared because of the shortage of an engineer of steam turbine, progress of technology or due to the environmental problem in recent years. So we tried to propose a decision-making system for building and operating LNG carriers by system dynamics. It turned out in a way that, compared to the Steam turbine system (S/T), Oil burning diesel engine with reliquefaction plant system (DRL) was cost advantageous assuming that the Boil-off gas price is equal to the LNG one.
Direct water injection (DWI) seems to be a promising solution for NOx reductions from marine diesels thanks to its wide flexibility in water injection. Its true potential, however, remains uncertain because both numerical and experimental investigations are necessary to determine the best injection pattern, which can balance greater NOx reduction and less thermal efficiency loss especially for two-stroke diesel engines with peripheral injector location. In this study, a double-needle single-injector type DWI system was tested in a two-stroke engine with peripheral injector layout to evaluate its NOx reduction capability under the existence of swirling flow. Its effect on flame temperature was investigated experimentally by flame temperature measurement and numerically by CFD simulation. It was found that injected water affected fuel spray penetration and its air entrainment around spray tip. For tested engine configuration, it is found simultaneous fuel and water injection was most effective in reducing NOx emission.