CNG buses were adopted in urban area as a promising alternative to old diesel buses which emitted lots of harmful emissions. Although CNG is able to meet the current emission standards, it is expected to be impossible to satisfy the requirements of the next EURO-6 emission regulation without an additional peripheral device. Hydrogen is known to be a gaseous fuel which features the wide flammability limit and the fast reactivity. A certain amount of hydrogen addition to CNG is able to extend the lean combustion range and produce lesser amounts of harmful emissions. In this research, the combustion and emission characteristics of HCNG(mixture of Hydrogen and CNG) fuel were experimented in an 11-liter heavy duty lean burn engine. The optimization of NOx reduction and fuel efficiency was investigated varying ignition timing for a fixed excess air ratio. The performance of a CNG oxidation catalyst was evaluated and the possibility of using a conventional CNG oxidation catalyst in an HCNG engine was also examined. The results show that the amounts of THC, CO, NOx are all reduced with the increase of spark timing retard from the MBT angle, and a CNG oxidation catalyst functions well on both CNG and HCNG fuel. However, since the efficiency of a CNG oxidation catalyst depends on the exhaust gas temperature, it is necessary to increase the exhaust gas temperature of an HCNG engine for better THC, CO conversions.
Lean bum was considered to overcome high thermal load and improve fuel economy in heavy duty SI engine. However, lean bum generally causes unstable engine operation due to combustion instability such as cyclic variation, misfire, or partial burning. To overcome such undesirable phenomena charge stratification inside the engine cylinder through fuel injection strategy was utilized and flow field enhancement through intake port and piston shape was adopted.
In this study, tile effects of swirl ratio and piston bowl shape on tile mixture preparation were investigated. High intensity of squish flow as well as swirl flow was acquired by the enlarged piston squish area and helical intake port. To obtain two dimensional fuel distribution planar ~laser induced fluorescence (PLIF) was used. Acetone was excited by KrF excimer laser (248nm) and its fluorescence image was acquired by ICCD camera. Fuel injection strategy with respect to the intake process was found to have the key role of tile whole stratification process. The intense squish flow was found to be effective to place relatively rich mixture to tile vicinity of spark plug in tile end period of compression process.
The pent-roof geometry of the cylinder head in a four-valve engine has been known to be favorable to the tumbling motion. The formation of a tumbling vortex is an effective way to enhance pre-ignition turbulence and it eventually promotes faster burning rates. This study presents experimental results of the tumble flow structure, including the flow motion phenomena, tumble mean velocity, angular momentum and turbulence intensity. Two four-valve cylinder heads were selected for changing tumble flow intensity and the tumble velocity was obtained under motoring conditions (at 1000rpm) by LDV measurement
HLPG fuel research has been started recently, which is obtained by adding hydrogen to the LPG fuel. The characteristics of the fuel LPG is stored in two phases in the fuel tank. Therefore, on-board vehicle reforming is suitable for LPG vehicle. Suitable methods for on-board reforming vehicle, does not require supply of water, small size and rapid response is available plasma partial oxidation method. So, in this study the characteristics of LPG fuel reforming using a plasma reactor are investigated. When the total flow rate of reformer inlet at 20~50lpm and supplied power is 200W, parametric effect of O2/C ratio, geometric designs of plasma reformer on the process were investigated. As a result of the experiment, the optimum condition of O2/C ratio for the highest H2 yield and H2 selectivity were determined to be 0.8 to 0.9 and 1.0 to 1.4 for reformer 1 and reformer 2 respectively. Highest H2 yield of both reformer 1 and reformer 2 condition were 20lpm(reformer 1; 20%, reformer 2; 34%), and highest H2 yield decrease as th total flow rate is increased.
EGR (Exhaust Gas Recirculation) system has been used 10 reduce NO, emissions, improve fuel economy, and decrease thermal loading of engine because it offers the benefits of charge dilution as is the case with a lean bum technique. It is currently used in conventional engines, especially light-duty gasoline and diesel engines for a variety of advantages, and in recent years, it has become as a means of reducing engine-out emissions for heavy-duty vehicles as a consequence of the development of its control schemes as well.
However, the occurrence of excessive cyclic variation with high EGR rates, especially at high load conditions, brings about the undesirable combustion instability within the engine cylinder, which results in the deterioration of both engine performance and emissions. Therefore, in order to avoid the reduction of thermal efficiency and to improve fuel economy, the optimum EGR rate depending on operating conditions of engine, should be derived effectively.
An experimental study was conducted to investigate the effects of EGR on performance and emission characteristics of a spark-ignition LPG fuelled engine, and the feasibility of an enhanced methodology, such as a cooled EGR system.
Lean burn was considered to overcome high thermal load and improve fuel economy in heavy duty SI engine with
large bore size. Fuel stratification in the cylinder was utilized to acquire the feasibility of lean burn. Measurement of
fuel distribution is one of the possible ways to identify the extent of fuel stratification. To obtain two dimensional fuel
distribution planar laser induced fluorescence (PLIF) was used. Acetone was excited by KrF excimer laser (248nm)
and its fluorescence image was acquired by ICCD camera.
In this study the effects of various parameters such as fuel injection timing, swirl ratio and piston bowl shape were
investigated. They were considered to have the direct effects on the mixture motion. Fuel injection strategy with
respect to the intake process was found to have the key role of the whole stratification process. The optimal value in
each parameter was sought that made the mixture well prepared for lean burn.
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