جستجوی مقالات مرتبط با کلیدواژه « Dual-Fuel » در نشریات گروه « مکانیک »

Today, with the help of simulation models, engine performance can be modelled with a high level of precision, and thereby various strategies for the improvement of engine performance including the use of dual-fuel mixtures can be investigated. In the present study, a multi-zone thermodynamic simulation-code in Gasoline-Natural Gas (NG) mode with a Blow-by sub-model and a NO predicting-mechanism was developed. Then using a single-cylinder research-engine, experimental data were collected from various cycles via the use of skip < /span>-fire technique at the compression ratio of 10 for the dual-fuel mixtures of 100%, 90%, 75% and 60% Gasoline and the rest NG. From the obtained experimental data, two 200-cycle series of motoring and combustion without residual-gases were provided to verify the simulation code. In the motoring mode, the results of the simulating code equipped with Blow-by sub-model were compared with the experimental results. Then in the combustion mode, the results of the simulation code were compared with the average of pressure-crank angle experimental data in each dual-fuel mode. The performance of the simulation code was confirmed with an error of less than 4%. Finally, the sub-model for the prediction of NO emission revealed that NO emission decreased with the increase of NG fraction.

Spark advance and fuel injection in proportion with inlet air into the engine combustion chamber are important factors in achieving complete combustion. In the current study, gasoline and NG injectors were calibrated and engine performance in dual fuel and single fuel modes were analyzed at the compression ratio of 10 and engine speed of 1500 rpm. The amounts of fuel injected by the injectors were measured in different modes and a calibration relationship for fuel injection was obtained for each of the injectors. The calibration results indicated that the pressure at injection location affected the amount of the fuel injected by the gasoline injector; however, no such changes were observed in the NG injector. The analysis of engine performance parameters demonstrated that engine torque and imep in gasoline single fuel mode were higher than those in gasoline-NG dual fuel mode, while the lowest values in this regard belonged to NG single fuel mode. Results also showed that HC and CO emissions increased with the increase of spark advance, the highest levels of which were observed in gasoline single fuel mode.

Spark-ignition (SI) engines are commonly used to produce the power needed for various purposes. Using gasoline-NG dual fuel in these engines and investigating the variations of burned residual gas from the previous cycle in combustion cycles can improve engine operating conditions. The experimental data for the current study were obtained from a single-cylinder SI engine in various spark advances at the compression ratio of 10 and engine speed of 1800 rpm in dual-fuel mode (consisting of mass fraction of 75% gasoline and 25% NG) and stoichiometric equivalence ratio in both skip fire and non-skip fire conditions. The obtained raw data were processed using a computer code to arrive at the in-cylinder pressure versus crank angle diagram and the indicated mean effective pressure. The analysis of ensemble average cycle diagrams obtained from the experimental cycles in optimum spark advances indicated that the in-cylinder pressure variations before peak pressure were greater in skip fire conditions and the difference between optimum spark advances in skip fire and non-skip fire conditions was calculated to be 9 crank angle degree. Standard deviation and coefficient of variations for the indicated mean effective pressure were lower in skip fire conditions; in other words, fewer cyclic variations were observed in skip fire conditions. Furthermore, mass fraction burn variations were higher in skip fire conditions as compared to a non-skip fire condition, which was indicative of faster combustion in the former.

In the present study, a single-cylinder research engine was utilized to capture experimental data at 9 compression ratio and 1800 rpm engine speed for dual fuel mixtures of 100%, 90%, 75% and 60% gasoline and the rest natural gas in skip-fire mode. Then, a gasoline- natural gas multi-zone thermodynamic entrainment simulation-code equipped with blow-by sub-model was developed. Two 200-cycle sets of free residual motoring and firing cycles were separated from the experimental data to check the response of the code. In motoring-case, the ensemble-average P-θ of the motoring set was compared with that of the code and the blow-by sub-model was verified. Next, in the firing-case, the results obtained from the code were compared with the ensemble-average P-θ of the firing set in each fuel combination and the code was validated. In the firing-case, the leakage to crevices was estimated to be considerably more than that of the motoring-case. In the firing mode of the code, the deviation of the obtained results of the code without blow-by option from the experimental results was more serious as compared to those of the code with blow-by, emphasizing the importance of the blow-by sub-model in the code.

Considering the disadvantages of gasoline and natural gas as mono-fuel in SI engines has made the researchers improve the performance and reduce the pollutant as the advantages of the application of dual-fuel engines. On the other hand, lean-burn in the engine may lead to reduced pollutants. In the present study various mixtures of gasoline and natural gas with the gasoline as the dominant fuel, including 100, 87.5, 75 and 62.5% in weight-base gasoline and the rest natural gas (respectively named as G100, G87.5, G75, G62.5) in lean-burn condition with 0.9 as the equivalence ratio are investigated. At 1800rpm and 10 compression ratio, cylinder pressure variations of 350 successive cycles of each mixture were recorded using a single-cylinder research engine. First of all, the raw data were processed and the optimized knock-free advance for each individual mixture was determined. Later on, the performance of all four mixtures in the corresponding optimized advance was explored. The results revealed that by increasing the amount of natural gas in the mixture, the CO pollutant reduced however the amount of HC initially increased which was followed by a decreasing trend. The amount of NOx had a direct relation with the appearance of the natural gas. In the lean-burn condition, a better performance was observed for G75 in comparison with G100 and the other mixtures.

The advantages and disadvantages of using gasoline and NG as single-fuel is a challenge for researchers in development of SI engines. Singular utilization of these fuels results in some advantages and disadvantages from economics, thermodynamics, pollution and development aspects and make it difficult to prefer one to the other. Assuming that using combination of the fuels can modify the output results, in the present research, different combinations of 100, 90, 75 and 60% gasoline and the rest of natural gas, designated as G100, G90, G75 and G60, were investigated in a SI single-cylinder engine at running at 1800rpm, 9 compression ratio and stoichiometric equivalence ratio. After collecting and processing in-cylinder experimental data in the combinations and different spark advances and their experimental data processing, consecutive cycle-to-cycle data were extracted and analyzed with engine output data. First, optimum spark advance of each combination was determined and then, the combinations were compared at their spark advances. The results revealed that increasing natural gas fraction in combination causes substantial reductions in standard deviation, σ, and coefficient of variation, COV of IMEP, so that σ and COV of G60 reduced by 51.6% and 49.2%, respectively, in comparison with G100. Reducing the gasoline presence in combination, the amount of CO2, NOx and HC reduced except G90 which have the higher HC and NOx, whereas, CO amount in G90 decreased to the lowest level. Also, no satisfactory performance was observed in the G90 combination.

One of the most efficient methods to reduce emissions and fuel costs of SI engines in petrol case, is the use of combined gasoline and NG. The ability of an engine is usually expressed with maximum power and maximum torque output of full-load state, but the operating time of the engines with full-load is less than that of part-load time. Therefore, studying the performance of the engine with a new mixed fuel (dual-fuel) requires studies under full-load and part-load. In the present work, dual gasoline-NG fuel with equal mass ratio together with single original fuel modes in full-load and a few part-load at 1800 rpm, 10.12 compression-ratio and almost stoichiometric equivalence-ratio have been taken into consideration in a SI single-cylinder research engine. In each load with a certain fuel, the spark advance was changed with 2°CAbTDC step and from obtained output and in-cylinder results, the optimum spark timing was determined for that mode and load. The results at optimum advance showed that increasing engine load, the exhaust gas temperature almost linearly for G100 and G0 but nonlinearly for G50 enhanced. Also, in full-load, the HC of the G100 appeared to be noticeably larger than those of G50 and G0. Decreasing engine-load for G100, HC amount reduced, while those for G50 and G0 increased. By changing the load, CO content for G50 and G0 fuels changed slightly, whilst that for G100 changed significantly. These observations emphasize a serious attention to dual fuel study mode in part-loads.