Combustion and Emission Enhancement of a Spark Ignition Two-Stroke Cycle Engine Utilizing Internal and External EGR Approach at Low-Load Operation

Two-stroke cycle engines have always been prominent due to their distinctive advantage incorporating high power-to-weight ratio, however the drawbacks are poor combustion efficiency, fuel short-circuiting and excessive emission of uHC and CO. These problems are apparent at low-load and speed regions and are the major obstacle to their global acceptance. The deficiencies can be addressed by increasing the in-cylinder average charge temperature employing Exhaust Gas Recirculation (EGR). An experimental study is conducted to investigate the influence of utilizing EGR techniques, including Internal and External EGR, on combustion misfiring occurrence, combustion stability and exhaust emissions using a single cylinder two-stroke SI engine at idling, low and mid-load conditions. From the results, it is observed since the average in-cylinder charge temperature is increased, due to utilizing EGRs, engine’s low and mid-load irregular combustions (misfire) and exhaust emissions are remarkably supressed and almost all of misfire cycles eliminated depending on the percentage of EGRs. In terms of combustion stability, it is agreed in general the application of EGRs improves the cyclic variation of IMEP, Pmax and CA10 compared to conventional operation. However, applying Ex-EGR compared to In-EGR will deteriorate cyclic variability of IMEP and CA10.The authors would like to acknowledge the Universiti Teknologi Malaysia (UTM) for financial support under the research university grant Q.J130000.3509.06G97

Effect of internal and external EGR on cyclic variability and emissions of a spark ignition two-stroke cycle gasoline engine

Conventional two-stroke cycle engine suffers from typical drawbacks including lower combustion efficiency and excessive emissions of uHC and CO which are largely due to low in-cylinder average charge temperature at low load and speed regions of engine operating conditions. Utilising the hot burned Exhaust Gas Recirculation (EGR) technique can boost the in-cylinder average charge temperature of the engine. The influence of hot burned gases applied by means of both Internal EGR and External EGR strategies on the combustion stability and exhaust gas emission of a single-cylinder two-stroke cycle engine running at low-load and mid-load of operating conditions was investigated experimentally along with simulation works using 1-D engine simulation code. The results indicated that both In-EGR and Ex-EGR improved the combustion stability (lower misfire cycle) and decreased the concentrations of uHC and CO emissions, specifically at low speed region; however, NOx concentration was increased. At Internal EGR setting of 30%, the Coefficient of Variation for maximum in-cylinder pressure (COVPmax) reached the minimum by 5.64 while when External EGR percentage was 25%, COVPmax approached about 6.67 at the mid-speed (2000 rpm) of engine operating condition

A tool for predicting the thermal performance of a diesel engine

This paper presents a thermal network model for the simulation of the transient response of diesel engines. The model was adjusted by using experimental data from a completely instrumented engine run under steady-state and transient conditions. Comparisons between measured and predicted material temperatures over a wide range of engine running conditions show a mean error of 7◦C. The model was then used to predict the thermal behavior of a different engine. Model results were checked against oil and coolant temperatures measured during engine warm-up at constant speed and load, and on a New European Driving Cycle. Results show that the model predicts these temperatures with a maximum error of 3◦C.Torregrosa, AJ.; Olmeda González, PC.; Martín Díaz, J.; Romero Piedrahita, CA. (2011). A tool for predicting the thermal performance of a diesel engine. Heat Transfer Engineering. 32(10):891-904. doi:10.1080/01457632.2011.548639S891904321

Evaluating the prevalence of numeric anomalies of primary teeth in 3-5 years children of Isfahan Kindergartens

1482 patients of 3-5 years ( 56% m/44% f) were selected from Isfahan kindergartens. In 1.4% of them, numeric  dental anomaly was diagnosed of which 0.74 %  had congenital missing teeth, 0.06 % had hyperdontia and 0.6% had geminated teeth. 0.72 % of Congenital missing was seen in boys while 1.2% in girls. Also, Gemination was seen 0.12 % in boys and 1.2% in girls which is 10 times more than boys in total study population. 0.2% of cases had concomitant tooth missing and gemination. Missing was mostly seen in mandibular incisors. Germination was seen  80% in mandibular anterior region. Besides, in 50% of the patients who had primary teeth missing, permanent teeth missing in both sides were also diagnosed by radiography. One case found with supernumerary tooth in maxillary lateral incisor region. In this article, the possible risk factors were analyzed in case and control groups. Any significant relationship between these factors and numeric dental anomalies was concluded

On the Spectral Convergence of the Supercompact Finite-Difference Schemes for the f-Plane Shallow-Water Equations

For the f-plane shallow-water equations, the convergence properties of the supercompact finite-difference method (SCFDM) are examined during the evolution of complex, nonlinear flows spawned by an unstable jet. The second-, fourth-, sixth-, and eighth-order SCFDMs are compared with a standard pseudospectral (PS) method. To control the buildup of small-scale activity and thus the potential for numerical instability, the vorticity field is damped explicitly by the application of a triharmonic hyperdiffusion operator acting on the vorticity field. The global distribution of mass between isolevels of potential vorticity, called mass error, and the representation of the balance and imbalance are used to assess numerical accuracy. In each of the quantitative measures, a clear convergence of the SCFDM to the PS method is observed. There is no saturation in accuracy up to the eighth order examined. Taking the PS solution as the reference, for the fundamental quantity of potential vorticity the rate of convergence to PS turns out to be algebraic and near-quadratic.</p