Experimental Investigation On Combustion And Emissions Characteristics Of A Hydrogen-blended Gasoline Engine

Improving the engine thermal efficiency and reducing the toxic emissions havebecome important in the development of internal combustion engines. Hydrogen isregarded as one of the most promising alternative fuels that can be applied by thespark-ignited engines. However, the pure hydrogen engines are prone to encounter theproblems of pre-ignition, backfire, deteriorated power output and adversely increasedNOx emissions. Comparatively, adding small amount of hydrogen and adjusting thehydrogen and traditional fossil fuel fractions in the total fuel according to the engineoperating conditions are capable of solving the contradictions between the mono fueland the frequently changed engine operating conditions. This paper investigated theeffect of hydrogen addition on the combustion and emissions characteristics ofgasoline engines through the theoretical analysis and experiments.Firstly, the effect of hydrogen addition fraction on the engine thermal efficiency,indicated mean effective pressure and cylinder pressure were analyzed based on thetheoretical model of spark-ignited engines. The results indicated that the engineindicated thermal efficiency was improved with the increase of hydrogen volumefraction in the intake at the same engine speed and load. However, because of the lowvolume energy density and high stoichiometric air-to-fuel ratio of hydrogen, theindicated mean effective pressure was decreased after the hydrogen blending.Meanwhile, the shape factor and efficiency factor in Weibe function were calibrated.Then, the calibrated Weibe function was adopted to evaluate the combustion processof hydrogen-blended gasoline engines. The results showed that the heat release rate,peak cylinder pressure and the degree of constant volume combustion were enhancedwith the increase of hydrogen volume fraction in the intake. A method for calculatingthe flame speed in the hydrogen-blended gasoline engines was proposed, which wasused to analyze the effect of hydrogen addition on the flame speed and radius of thefuel-air mixtures in the cylinder. The results confirmed that the addition of hydrogenwas effective on enhancing the flame speed and reducing the post combustion ofgasoline engines.Based on the theoretical analysis results, the strategy of “coordinative control offuel and operating conditions” was proposed for the hydrogen-blended spark ignitionengines. According to this strategy, at the cold start and warming up conditions, theengine is fueled with the pure hydrogen; at the idle and part load conditions, theengine is fueled with the hydrogen-high octane number fuel blends; at the high speedand load conditions, the engine can be fueled with the pure high octane number fuels.The effect of hydrogen addition on the combustion and emissions characteristics of the gasoline engines under various engine operating conditions were firstinvestigated on the engine test bench. The experimental results confirmed that HC andCO emissions during the cold start were effectively reduced after the hydrogenblending. Moreover, at the idle and part load conditions, the addition of hydrogencontributed to the elevated indicated thermal efficiency, shortened flame developmentand propagation periods, decreased cyclic variation and extended lean burn limit. Atan engine speed of1400r/min, an intake manifolds absolute pressure of61.5kPa anda constant spark timing of22°crank angle before the top dead center, the relevantexcess air ratio for the lean burn limit was raised from1.45to1.55,1.97and2.55when the hydrogen volume fraction in the intake was increased from0to1%,3%and4.5%, respectively. The effects of excess air ratio, spark timing, engine load andcylinder closure on the combustion and emissions performance of thehydrogen-blended gasoline engine were also investigated. The test results showed thatthe properly increased excess air ratio benefitted reducing HC, CO and NOxemissions. At the idle and low load conditions, the engine cooling loss and toxicemissions were further decreased after the cylinder cutoff. Besides, it was also foundthat the engine could gain the best fuel economy at the idle condition throughhydrogen addition and cylinder cutoff. The engine idle energy consumption wasreduced from27.28MJ/h of the original engine to16.35MJ/h of the6.63%hydrogen-blended gasoline engine with two-cylinder cutoff, which was decreased byabout40.1%. Furthermore, it was also confirmed that the effect of hydrogen additionon enhancing the engine performance was more pronounced at the low load and leanconditions.Since the electrolysis of water generates hydrogen and oxygen together, thispaper also compared the effects of hydroxygen addition on the combustion andemissions characteristics of the gasoline engine. The test results indicated that theeffect of standard hydroxygen addition on improving the engine thermal efficiencyand reducing HC and CO emissions was more pronounced than the hydrogen additionat the same hydroxygen and hydrogen addition fractions under the lean conditions. Atthe same time, it was also found that increasing the hydrogen volume fraction in thehydroxygen was helpful on reducing the engine particulate emissions.A1.8L hydrogen-blended gasoline engine powered Elantra vehicle was invented.A strategy for producing the hydrogen through onboard hydrogen generator wasproposed, a water electrolyzer was mounted on the trunk of the test vehicle to producehydrogen by the extra power of the engine generator. Thus, the test vehicle realizedthe onboard hydrogen production and storage. According to the regulated testingprocedure given by GB18352.3-2005, the emissions performance and fuel economyof the hydrogen-blended gasoline engine powered vehicle was investigated on achassis dynamometer. The test results indicated that, compared with the vehicle powered by the original gasoline engine, the vehicle fuel economy was improved andtotal HC and CO emissions during the driving cycle were reduced by64.1%and62.1%when the engine was powered by the hybrid hydrogen gasoline engineaccording to the “coordinative control of the fuel and operating conditions”.