Research On Fuel And Air Parameters Joint Optimization Of Regulated Two-stage Turbocharged Diesel Engine At Different Altitudes

In order to improve the plateau adaptability of diesel engine,regulated two stage turbocharging system was applied to replace the original single stage turbocharging system,and full load characteristics of the engine at different altitudes was calibrated.But there was still improvement space of power performance at most operation points due to the limitation of test conditions.This paper focused on the theme of "power increase of regulated two stage turbocharged diesel engine",and optimized the injection mass per cycle,injection timing and bypass valve angle at different altitudes under the premise of satisfying reliability constraints.Firstly,flow field of the bypass valve was simulated to get the discharge characteristic with Fluent.According to the simulation result,the discharge coefficient was more sensitive to the valve angle under small valve angle.Secondly,based on the original single stage turbocharged diesel engine model,regulated two stage turbocharged diesel engine model was put forward,which was checked by matching the simulation result with the experiment data.And the relationship between the performance parameters,constraint parameters and injection mass per cycle,injection timing and bypass valve angle was determined by simulation.According to the result,with the change of injection mass per cycle or injection timing alone,turbo inlet temperature and both two stage turbocharger speed presented similar change rule;and with the change of injection mass per cycle,injection timing or bypass valve angle alone,both two stage turbocharger speed presented similar change rule.Finally,the optimization problem was simplified according to the relationship between fuel-air parameters and performance parameters,constraint parameters.Based on fuzzy control theory,a fuel and air parameters optimization algorithm was put forward.Then the fuzzy optimization algorithm and diesel engine performance coupling simulation model was set up and full load characteristics of the engine at altitudes of 0m,2000 m,3000m and 4500 m was optimized to get the best fuel and air parameters,and the rationality of these optimized result was verified.Took 2100 rpm at 0m altitude for example to analyse the whole optimization process.The full load optimization results at different altitudes were restrained by the maximum cylinder pressure and turbo inlet temperature,and there was certain margin of both stage turbocharger speed.Compared with the original performance,there was significant increase of engine power at all operation points.At operation point of 2100 rpm at 4500 m,the engine power was increased from 256.5kW to 319.6kW by 24.6%,the fuel consumption was reduced from 243.1g/kWh to 222.3g/kWh by 8.6%.With the increase of altitudes and engine speed,the best injection mass per cycle decreased and the best injection timing increased,while the rule of best valve angle becomed complicated due to the coupling influence of AF ratio and pumping loss.