The continuous increase in the number of stringent exhaust emission legislations of marine Diesel engines had led to a decrease in NO_x emissions at the required level. Selective catalyst reduction (SCR) is the most prominent and mature technology used to reduce NO_x emissions. However, to obtain maximum NO_x removal with minimum ammonia slip remains a challenge. Therefore, new mixers are designed in order to obtain the maximum SCR efficiency. This paper reports performance parameters such as uniformity of velocity, ammonia uniformity distribution, and temperature distribution. Also, a numerical model is developed to investigate the interaction of urea droplet with exhaust gas and its effects by using line (LM) and swirl (SM) type mixers alone and in combination (LSM). The urea droplet residence time and its interaction in straight pipe are also investigated. Model calculations proved the improvement in velocity uniformity, distribution of ammonia uniformity, and temperature distribution for LSM. Prominent enhancement in the evaporation rate was also achieved by using LSM, which may be due to the breaking of urea droplets into droplets of smaller diameter. Therefore, the SCR system accomplished higher urea conversion efficiency by using LSM. Lastly, the ISO 8178 standard engine test cycle E3 was used to verify the simulation results. It has been observed that the average weighted value of NO_x emission obtained at SCR outlet using LSM was 2.44 g/kWh, which strongly meets International Maritime Organization (IMO) Tier III NO_x (3.4 g/kWh) emission regulations.

Marine diesel engines are extensively used for transportation and as well as for power generation purpose because of its high durability, thermal and fuel efficiency than the gasoline engines. But the marine diesel engine produced severe NOx emissions that are currently well discussed issue needed to be solved due to its serious health and environmental problems. At the same time, because of increasing stringent regulations of NOx emissions it is necessary for ships to meet the international maritime organization (IMO) Tier III regulations in NOx emission control areas (ECA). It is enforced for the vessels that are constructed on and after the 1st January 2016. Therefore, a demand for well functioning NOx reduction technology is required. Currently SCR is the most dominant and mature technology used to reduce the NOx with ammonia over the SCR catalyst. SCR catalyst is the core part of SCR system; hence this review described the different types of catalysts and their behavior under different conditions. Furthermore, the deactivation of SCR catalyst occurs by different mechanisms; however, the most significant mechanism is sulfur poisoning. Reaction temperature and availability of ammonia is also significant parameter for sulfur poisoning. Therefore it is necessary to investigate how sulfur behaves with SCR catalysts. Even though many studies have been performed on sulphur poisoning of catalysts but still requires complete understanding. This review covers the sulfur poisoning of vanadium and Cu-zeolites based SCR catalysts with mainly focus on Cu-zeolites because of its sulfur sensitivity.

In this article we research about underwater acoustics transceivers. As Underwater acoustic transceivers consume more power than Radio frequency transceivers. The techniques which are being utilized in radio frequency cannot be implemented directly in underwater acoustic system it needs to be re investigated to design new methods. To achieve reliable acoustic data transmission new techniques should be achieved or the traditional Orthogonal frequency divisional multiplexing techniques should be revised. The power consumption also relies upon underwater acoustic signal propagation and transmission distances. Several underwater acoustic applications require long-term monitoring of the sea. For the battery powered modems, it becomes very serious problem. By designing an Energy efficient OFDM Communication system we can solve this problem. We study about peak to average power ratio in an Orthogonal frequency divisional multiplexing system by reducing the major draw-back of OFDM system. The PAPR reduction utilized in this paper is Partial Transmit Sequences for underwater acoustic OFDM communication system which has lesser complexity. The results have provided better performance in underwater acoustic OFDM communication system.