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The vibration of the ignition frequency component of the engine during idling causes driver discomfort. To minimize this, an optimal exhaust system with a variable device that can exert optimal pressure is required. In this study, the geometry of the variable device was designed in orifice and cylinder types. Next, the designed variable devices were implemented in a conventional exhaust system with an X chamber. A comparative analysis was conducted to propose an optimal geometry through back-pressure and vibration measurements. During the experiment, the orifice geometry exhibited higher back pressure than the conventional geometry and a large difference in back pressure before and at the exhaust gas merging position. Furthermore, the orifice geometry showed a 2.56% increase in the vibration of the 1X component in the Y-axis direction. By contrast, the cylinder geometry exhibited slightly higher back pressure than the conventional geometry and the smallest difference in back pressure before and at the exhaust gas merging position. The cylinder geometry showed a 2.45% reduction in the vibration of the 1X component in the Y-axis direction. [ABSTRACT FROM AUTHOR]

In this study, a pressure transducer was installed in an exhaust system to analyze the effect of the change in back pressure according to the change of the confluence geometry of an exhaust pipe system on an exhaust emission. In addition, to perform exhaust gas measurement, the system was warmed up for about 40 s on the chassis dynamometer, and exhaust gas and back pressure measurements were performed simultaneously. In the back pressure measurement results, it was possible to confirm the difference in back pressure according to the change in the confluence shape. In addition, it was also confirmed that there was a clear difference in the exhaust emission measurement result. In particular, the H-type exhaust pipe system showed the highest pressure in the exhaust pipe due to the influence of the confluence geometry. Due to this influence, THC showed the highest measured value in the exhaust emission result. However, the X-type exhaust pipe system showed the lowest pressure due to the influence of the confluence geometry. Due to this influence, the THC showed the lowest measured value in the exhaust emission result. Therefore, through the conclusion of this study, an optimal exhaust system to reduce THC was proposed, and the importance of back pressure in exhaust system design was confirmed. [ABSTRACT FROM AUTHOR]

The vibration of the ignition frequency component of the engine during idling causes driver discomfort. To minimize this, an optimal exhaust system with a variable device that can exert optimal pressure is required. In this study, the geometry of the variable device was designed in orifice and cylinder types. Next, the designed variable devices were implemented in a conventional exhaust system with an X chamber. A comparative analysis was conducted to propose an optimal geometry through back-pressure and vibration measurements. During the experiment, the orifice geometry exhibited higher back pressure than the conventional geometry and a large difference in back pressure before and at the exhaust gas merging position. Furthermore, the orifice geometry showed a 2.56% increase in the vibration of the 1X component in the Y-axis direction. By contrast, the cylinder geometry exhibited slightly higher back pressure than the conventional geometry and the smallest difference in back pressure before and at the exhaust gas merging position. The cylinder geometry showed a 2.45% reduction in the vibration of the 1X component in the Y-axis direction.

Recently, the driving performance that maximizes driving pleasure, exhaust sound quality, and quietness have been recognized as important elements according to the demands of clients. Technology has been dramatically developed while the evaluation and improvement of the exhaust system have been attempted using various methods to meet the requirements of clients, the largest problem in designing the exhaust system is to maximize performance by forming the optimal back pressure and flow velocity and to reduce the generated noise and vibration. The objective of this study is to propose an optimal geometry of an exhaust system for sports sedans with a V6 and above engine. To achieve this, an experiment was conducted as follows. Before a prototype was fabricated, an exhaust system was designed and the fluid flow was analyzed. A pressure transducer was installed in the prototype, and the exhaust pressures on the exhaust system were measured at idle, medium and high engine speeds. Noise and vibration were also measured to analyze the impact of confluence geometry on the silence of vehicle. Finally, wheel horsepower, torque from wheels were analyzed using a chassis dynamometer to identify an output difference according to confluence chamber geometry and propose an optimal geometry. [ABSTRACT FROM AUTHOR]

In this study, a pressure transducer was installed in an exhaust system to analyze the effect of the change in back pressure according to the change of the confluence geometry of an exhaust pipe system on an exhaust emission. In addition, to perform exhaust gas measurement, the system was warmed up for about 40 s on the chassis dynamometer, and exhaust gas and back pressure measurements were performed simultaneously. In the back pressure measurement results, it was possible to confirm the difference in back pressure according to the change in the confluence shape. In addition, it was also confirmed that there was a clear difference in the exhaust emission measurement result. In particular, the H-type exhaust pipe system showed the highest pressure in the exhaust pipe due to the influence of the confluence geometry. Due to this influence, THC showed the highest measured value in the exhaust emission result. However, the X-type exhaust pipe system showed the lowest pressure due to the influence of the confluence geometry. Due to this influence, the THC showed the lowest measured value in the exhaust emission result. Therefore, through the conclusion of this study, an optimal exhaust system to reduce THC was proposed, and the importance of back pressure in exhaust system design was confirmed.

This study discusses a novel approach toward homogeneous charge compression ignition operation in the 5 - 10 bar net indicated mean effective pressure range. This approach is based on the combination of boosting and variable valve actuation to maximize engine efficiency. Compression ratio plays a key role and determines low-temperature combustion feasibility in modern gasoline compression ignition concepts. In order to explore the interactions between compression ratio, boosting system and variable valve actuation, multi-cylinder engine models were utilized which employed the University of Michigan combustion model. Valve strategies featured switching from low-lift negative valve overlap to high-lift positive valve overlap, and the switching point was found to be dependent on compression ratio. A recent study by the authors suggested that heating the charge from external compression is more efficient than heating by residual gas retention strategies. Use of non-cooled intake air allows for valve events and combustion phasing that promote turbocharger performance and alleviate the backpressure problems often associated with low temperature combustion engines. Elevated intake pressure and reduced pumping work allow for improvements in efficiency with minimal NOx formation and acceptable ringing. It was found that further efficiency benefits can be realized by increasing compression ratio. Identification of trade-offs between engine hardware and combustion mode appears to be critical for homogeneous charge compression ignition operation in the 5 -10 bar net indicated mean effective pressure range. By focusing on this operating range, the present modeling study attempts to shed some light on practical applications of light-duty gasoline compression ignition concepts. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Altering the cam with a decreased valve overlap decreases torque at the lean limit. [•] THC and the CH4 reductions are approximately 41% for the HCNG fuel with reduced valve overlap. [•] The NO x from the camshaft with decreased valve overlap is higher than that of original camshaft. [ABSTRACT FROM AUTHOR]

In a gasoline SI engine, valve events and spark timings put forth a major influence on overall efficiency, fuel economy, and exhaust emissions. Residual gases controlled by the valve overlap can be used to reduce NOx emissions and the spark retardation technique can be used to improve raw THC emissions and catalyst light-off performance during the cold start phase. This paper investigated the behaviors of the engine and its combustion characteristics with various intake valve timings and spark timings during the fast idle condition and cold start. And cyclic THC and NOx emissions were measured at the exhaust port and their formation mechanisms were examined with fast response gas analyzers. As a result, THCs and NOx were reduced by 35% and 23% with optimizing valve overlap and spark advance during the cold transient start phase. Consequently, the valve events and ignition timings were found to significantly affect combustion phenomena and cold-start emissions. [ABSTRACT FROM AUTHOR]

In internal combustion engines, particularly for spark ignition (SI) engines, valve events and their timings have a major influence on the engine's overall efficiency and its exhaust emissions. Because the conventional SI engine has fixed timing and synchronization between the camshaft and crankshaft, a compromise results between engine efficiency, performance, and its maximum power. By using variable valve timing (VVT) technology it is possible to control the valve lift, phase, and valve timing at any point on the engine map, with the result of enhancing the overall engine performance. To get full benefits from VVT, various types of mechanisms have been proposed and designed. Some of these mechanisms are in production and have shown significant benefits in improving engine performance. During the last two decades, remarkable developments have been seen in the field of VVT. This paper reviews the literature in the technology of intake and exhaust philosophies of VVT and their effects on the pressure–volume (PV) cycle of the engine. A single-cylinder engine is simulated by the GT-Power software. The effects of different VVT philosophies from the simulations are analysed and compared to those of the literature reviewed. [ABSTRACT FROM AUTHOR]

• There was almost no methanol leakage at the small valve overlap in DMDF engine. • Formaldehyde emissions derived from the unburned formaldehyde in the cylinder. • The increase of valve lift during valve overlap was main cause of methanol leakage. • The experimental results in marine engine were consistent with the simulation. The diesel methanol dual fuel (DMDF) engine is confronting with the problem of high unregulated emissions of methanol and formaldehyde. The previous studies on unregulated emissions of DMDF engine focused on the measuring methanol and formaldehyde concentrations in the exhaust without distinguishing whether emissions come from leakage during valve overlap or incomplete combustion in the cylinder. In this study, a computation fluid dynamics (CFD) model coupled with a detailed chemical kinetic mechanism was developed to investigate the methanol and formaldehyde emissions of DMDF engine. The results showed that the unburned methanol and formaldehyde in the cylinder were the main part of the total methanol and formaldehyde emissions based on the 41 °CA valve overlap of simulation model. Then the effects of different intake valve opening (IVO) and exhaust valve closing (EVC) on methanol emissions were investigated. The results showed that only increasing IVO or EVC had very little effect on the leakage of methanol during scavenging. However, when the IVO and EVC changed simultaneously, the valve lift would significantly increase during the valve overlap of scavenging, which had a great impact on methanol leakage. The simulation results were validated by experiments in a 6170 marine engine. The experimental results were consistent with the simulation results and the increase of effective flow area caused by valve lift during large valve overlap was the most important reason for the increase of methanol emission. Therefore, all engines have almost no leakage in small valve overlap. However, with the increase of valve overlap, the actual results were different due to the different valve lift and mixture concentration of different engines. [ABSTRACT FROM AUTHOR]

A detailed investigation of ignition and injection timing influence on post-oxidation phenomenon which in-turn can improve turbo-performance along with the emissions of a turbocharged (SI) engine. In this research a novel methodology by adopting the scavenging-based post-oxidation phenomenon was investigated. Firstly, 1-D simulation model was developed, and the model was validated with the experimental results. Then, the simulation was used for the investigation of ignition and injection timing influence on post-oxidation. Thereafter, experimental tests for the post-oxidation were conducted. From the results, it can be stated that the retard of ignition timing shifts the combustion phase towards late which increased the exhaust pressure and temperature. This could increase the chances of the actuation of the post-oxidation reaction in the exhaust manifold. Moreover, it was also found that the injection of fuel during the overlap phase and after overlap had significant influence on the post-oxidation process. Fuel injection during the overlap can increase the possibility of scavenging a fraction of fuel and promote post-oxidation reaction. In both cases, it was found that the emissions and turbo-performance become better at late spark and early injection timing due to oxidation reaction. However, thermal efficiency was affected which will be optimized in the future. • Influence of ignition and injection timing on post-oxidation were characterized. • Retarding of spark timing leads to better post-oxidation phenomena. • Retarding of spark and advance of injection timing shows better emissions and turbo-lag. • Further injection advancing leads to fuel losses with scavenged air. • Thermal efficiency shows reverse effect due to fuel losses in scavenging phenomena. [ABSTRACT FROM AUTHOR]