A review study on diesel and natural gas and its impact on CI engine emissions

Diesel engines produce high emissions of nitrogen oxide, smoke and particulate matter. The challenge is to reduce exhaust emissions but without making changing their mechanical configuration. This paper is an overview of the effect of natural gas on the diesel engine emissions. Literature review suggests that engine load, air-fuel ratio, and engine speed play a key role in reducing the pollutants in the diesel engine emissions with natural gas enrichment. It is found that increasing the percentage of natural gas (CNG) will affect emissions. Nitrogen oxide (NOx) is decreased and increased at part loads and high loads respectively when adding CNG. The reduction in carbon dioxide (CO2), particulate matter (PM) and smoke are observed when adding CNG. However, carbon monoxide (CO) and unburned hydrocarbon (HC) are increased when CNG is added

CFD investigation of transonic axial compressor rotor blade at various off-design conditions

Flow separation over blade surfaces is an important parameter and its reduction or elimination can improve better aerodynamic performance, efficiency and stall margin. In this work, numerical investigation has been carried out to study the flow separation and performance analysis of a transonic axial compressor rotor blade at off-design operating conditions. The off-design cases studied comprised of compressor operation at 80%, 90%, 100% and 105% on the on-design rotational speed. The results are validated with experimental work from literature. Additionally, 3D flow visualisations and performance parameters were examined in detail to understand the blade to blade relative mach number distributions and shock front created by the model. Finally, the benefits of unsteady simulation on axial compressor blade performance predictions were examined

Flow modification around a circular cylinder applying splitter plates

A number of different studies were reviewed to investigate the functionality of splitter plates for the purpose of drag reduction and vortex elimination behind a circular cylinder. The studies were carried out numerically or experimentally in different combinations of Reynolds range, 2D or 3D dimensions, with intention of drag reduction, vortex suppression or both. Results were compared to discover the generalities of a splitter plate's applications and its performance in drag reduction and vortex control. The reduction of 12% up to 38.6% in drag coefficient suggests that all reviewed studies verified the effectiveness of upstream plate in drag reduction. Varied upstream plate's gap ratios (gap between the plate and cylinder) were tested and the optimum position was obtained. For the finite cylinder case, however, the studies discovered that the effectiveness of upstream plate decreased severely and thus, are barely considered as a drag reductive tool for shorter cylinders. Although downstream plate influences drag force, its prominent application is found to be vortex shedding elimination (up to 14.7%). The length ratio and gap ratio of downstream plate were varied in these studies and it was found that the length ratio was a more important factor compared with the gap ratio in the case of vortex suppression

Hybrid mesh for nasal airflow studies

The accuracy of the numerical result is closely related to mesh density as well as its distribution. Mesh plays a very significant role in the outcome of numerical simulation. Many nasal airflow studies have employed unstructured mesh and more recently hybrid mesh scheme has been utilized considering the complexity of anatomical architecture. The objective of this study is to compare the results of hybrid mesh with unstructured mesh and study its effect on the flow parameters inside the nasal cavity. A three-dimensional nasal cavity model is reconstructed based on computed tomographic images of a healthy Malaysian adult nose. Navier-Stokes equation for steady airflow is solved numerically to examine inspiratory nasal flow. The pressure drop obtained using the unstructured computational grid is about 22.6 Pa for a flow rate of 20 L/min, whereas the hybrid mesh resulted in 17.8 Pa for the same flow rate. The maximum velocity obtained at the nasal valve using unstructured grid is 4.18 m/s and that with hybrid mesh is around 4.76 m/s. Hybrid mesh reported lower grid convergence index (GCI) than the unstructured mesh. Significant differences between unstructured mesh and hybrid mesh are determined highlighting the usefulness of hybrid mesh for nasal airflow studies

A review on the impact of aircraft cabin air quality and cabin pressure on human wellbeing

Airliner cabins present more complicated scenario due to different design and operation challenges owing to the extreme environmental conditions, complexity of the operational systems, and the authorities that govern such environments. The scientific evaluation is rendered difficult due to lack of empirical evidence determining the airliner cabin air quality as well as consequent health effects occurring due to short or long flight exposure. Crew members and passengers report dizziness, fatigue, headaches, sinus and ear problems, dry eyes and sore throats during and after travel. There are persistent concerns about the transmission of infectious agents such as influenza, tuberculosis and measles viruses during flights. Moreover, a systematic collection of data related to airplane environmental exposures is not yet available and the effects of environmental conditions on wellbeing of travelers and their comfort level are yet to be fully ascertained. In this work, a systematic review of the air quality inside the airliner cabin are discussed. The potential pollutants and their established causes are discussed. In addition to this, major health discomforts faced by the occupants are presented

A review on the micro energy harvester in Structural Health Monitoring (SHM) of biocomposite material for Vertical Axis Wind Turbine (VAWT) system: a Malaysia perspective

The usage of wind energy as a form of renewable energy is becoming increasingly popular year by year. This technology has been applied widely in several regions in the world and already reached maturity in terms of technology, infrastructure and cost competitiveness. The performance of the wind turbine system depends upon factors such as design, aerodynamic performance and material selection. Thus, Structural Health Monitoring (SHM) has become crucial in evaluating the performance of wind turbine in real time. Furthermore, the application of smart material in SHM can be utilized as micro energy harvester as well. Nonetheless, the application of SHM in Malaysia׳s climate for wind turbine is still premature, especially in the approach biocomposites material towards its blade system. Several issues are highlighted in this paper such as Vertical Axis Wind Turbine (VAWT), biocomposites material selection and the issue in the micro energy harvester as well. The issues are discussed and compared with the recent finding in this review. Several recommendations are suggested for future studies in benefiting the Malaysian especially on the application of wind energy to promote better green technology for tomorrow

Cryogenic pipe flow simulation for liquid nitrogen with vacuum insulated pipe (VIP) and Polyurethane (PU) foam insulation under steady-state conditions

Cryogenics is concerned with working with fluids at very low temperatures; less than 120 K. Cryogenic pipe flow is very different compared to normal fluid pipe flow in terms of evaluation and analysis due to the fluid state change that is caused by a heat leak in cryogenics during transportation through the transfer line. As the cryogenic system is necessarily immersed in insulation, it becomes more difficult to access. Numerical solutions and computational fluid dynamics (CFD) simulations that are non-disruptive and relatively low in cost are an advanced alternative for studying cryogenic systems. The present study reports the liquid nitrogen pipe flow simulation for process pipe with vacuum insulated pipe (VIP) and with Polyurethane (PU) foam insulation to understand the temperature distribution in the pipe flow under steady-state conditions. The 3-dimensional liquid nitrogen pipe flow simulation has been conducted using ANSYS FLUENT software. The temperature distributions resulting from the liquid nitrogen pipe flow simulation with VIP are within the range of 77.0 K to 82.1 K for inlet volume flow rates from 250 LPH to 2000 LPH. The optimum result in terms of the temperature distributions was produced from the liquid nitrogen pipe flow simulation with VIP

A two-component CFD studies of the effects of H2, CNG, and diesel blend on combustion characteristics and emissions of a diesel engine

Numerical simulations were conducted on a Ricardo Hydra diesel engine which is single cylinder engine and uses direct injection method. This study was performed by using a two-dimensional CFD code to examine the combustion characteristics and emissions of a diesel engine in diesel-CNG and diesel-H2 dual-fuel operations, as well as in the diesel-CNG-H2 tri-fuel operation at various air-fuel ratios. The results indicate that the peak in-cylinder pressure and peak temperature were increased with the addition of gaseous fuels at low and medium values of exceeds air. Compared with Diesel-H70-N30 for tri-mode and Diesel-H2 for dual mode, it is observed that there were no effects on the peak temperature at high exceed air. At 2.4 exceed air, the peak pressure increases by means of adding the limit value of hydrogen, such as H30-N70 and H50-N50, to CNG and it begins to decrease with H70-N30 and H2-Diesel operations. Diesel-H2-CNG operations decrease CO/CO2 emissions compared with Diesel-CNG operation and decrease NO emission compared with Diesel-H2 operation at every exceed air. The reduction in CO/CO2 emissions was suggested at high hydrogen fraction in CNG (H70-N30) with all exceeds air whereas low hydrogen fraction in CNG (H30-N70) can repress uncontrolled hydrogen combustion and further limit the increment of NO emission

Heavy metal concentrations (CD, CU, NI, PB, FE AND ZN)in the different soft tissues and shells of pholas orientalis collected from Sekinchan and Pantai Remis, Selangor.

The clam, Pholas orientaliswere collected from the mudflats of Sekinchan and Pantai Remis, and their soft tissues were dissected into crystalline style, siphon, mantle and foot; while the shells were divided into three parts namely the umbo, smooth part (anterior of shell) and rough part (posterior of shell). Generally, the results show that: 1) All the different soft tissues accumulated higher concentrations of essential Cu, Zn and Fe when compared to those in the hard tissues; 2) On the other hand, the three hard tissues accumulated higher concentrations of nonessential Cd, Ni and Pb than those in the soft tissues. These results reflected a different binding affinity for the two different metal groups between the soft and the hard tissues; 3) The different levels of metals found within the four different tissues indicated that metal detoxification mechanism in the different organs are not similar in P. orientalis. The ecological distribution and metal distribution in the different tissues of P. orientaliscan serve as a baseline for future reference

Turbulence model selection for low Reynolds number flows

One of the major flow phenomena associated with low Reynolds number flow is the formation of separation bubbles on an airfoil’s surface. NACA4415 airfoil is commonly used in wind turbines and UAV applications. The stall characteristics are gradual compared to thin airfoils. The primary criterion set for this work is the capture of laminar separation bubble. Flow is simulated for a Reynolds number of 120,000. The numerical analysis carried out shows the advantages and disadvantages of a few turbulence models. The turbulence models tested were: one equation Spallart Allmars (S-A), two equation SST K-ω, three equation Intermittency (γ) SST, k-kl-ω and finally, the four equation transition γ-Reθ SST. However, the variation in flow physics differs between these turbulence models. Procedure to establish the accuracy of the simulation, in accord with previous experimental results, has been discussed in detail