Experimental Study On Performance Of A Hybrid Syngas-gasoline Engine Based On Waste Heat Recovery

In recent years, the increased energy crisis and air pollution restrict economicdevelopment of countries around the world. Therefore, the work for improving theutilization ratio of energy and looking for green, clean and renewable energy is urgent.The continuous development of auto industry improves people’s life quality. But italso increases the dependence on fossil fuels and caused environmental pollution. Forimproving the thermal efficiency and reducing toxic emissions of internal combustionengines, the new energy development has become the focus of many researchers.As a kind of renewable and alternative energy carrier, hydrogen helps ease thedependence on fossil fuels. Compared with gasoline and diesel, hydrogen has manypositive physicochemical properties, such as lower ignition energy density, fasterflame speed and shorter quenching distance. However, since the energy density ofhydrogen on volume basis is much lower than that of gasoline and diesel, purehydrogen engines are prone to produce lower power output than gasoline or dieselengines. Compared with the pure hydrogen engines, using a small amount ofhydrogen as an additive to gasoline engines can not only reduce the engine fuelconsumption and toxic emissions, but also ensure the power output at part loadconditions. But the limited hydrogen infrastructure distribution and risks in hydrogenstorage and transportation are still barriers for the commercialization ofhydrogen-blended engines.Compared with hydrogen, ethanol is a kind of renewable energy resource, whichcan be easily derived from biomass. Besides, ethanol also gains other good properties,such as easy transport, biodegradability and low toxicity. Comparatively, using therelatively safe ethanol instead of hydrogen and producing syngas by fuel reforming isa feasible strategy. It can not only ensure the supply of hydrogen and solve theproblems of storage and transportation, but also ensure the power output at part loadconditions. Moreover, the onboard catalytic fuel reforming can recover the waste heatfrom the engine exhaust to produce syngas. Then the syngas and gasoline areintroduced into the cylinder to realize the combustion of the syngas-gasoline mixture.And the syngas could be used to improve the combustion and emissions performancesand enhance the thermal efficiency of engines.Firstly, the basic fuel reforming experiments were carried out in the study. Variousfeedstocks of reforming such as methanol, ethanol, n-heptane and isooctane were used.Two different types of catalysts: noble metal catalyst Pt/CeZrO₂/Al₂O₃and non-noblemetal catalyst Cu-Zn/Al₂O₃-ZrO₂were applied. Two kinds of reforming methods:steam reforming and catalytic decomposition were utilized. The best scheme forvehicle application was found by comparing different experimental results, including reaction temperature, water/feedstock molar ratio, space velocity and feedstock flowrate.Then, according to the heat transfer and chemical design technology, a fuelreforming reactor was designed and fabricated. The reactor was essential to realize theonboard hydrogen production by fuel reforming. The design principles mainly includetwo aspects. On the one hand, part of waste heat was transferred to feedstocks asmuch as possible. The feedstocks were rapidly transformed from the liquid phase intogaseous phase. Another part of waste heat was transferred to the catalyst to ensure thatthe catalyst had higher activity and produced syngas efficiently. On the other hand,the reactor should be as compact as possible to match the engine.Finally, the syngas-blended engine experiments based on waste heat recovery wereconduced. The effect of syngas addition on performance of a spark-ignited gasolineengine by ethanol steam reforming at stoichiometric condition was invetigated. Thetest results showed that the high performance of enthanol steam reforming wasachieved with the waste heat recovery. Ethanol conversion and hydrogen concentrationincreased with the increase of exhaust temperature. Meanwhile, the indicted thermalefficiency was improved after the syngas addition. The peak cylinder pressure and theengine working capability were elevated with the increase of syngas addition fractionat lean condition. The the coefficient of variation in indicated mean effective pressurewas decreased and the engine lean burn stability was improved with the syngasenrichment. Compared with gasoline, the hydrogen and carbon monoxide in thesyngas had higher flame speeds. The flame development and propagation periodswere reduced after the syngas blending. The syngas was produced and stored with thewaste heat recovery. Then the effect of syngas addition on performance of aspark-ignited gasoline engine by ethanol reforming at cold start condition wasinvetigated. The test results showed that the indicated mean effective pressure andengine speed were increased with syngas addition because the hydrogen and carbonmonoxide in the syngas have low igniton energies. In addition, since hydrogen andcarbon monoxide in syngas had wide flammabilities and a high flame speeds, thecombution in cylinder was improved and the toxic emissions were decreased.