Miller Cycle with Early Intake Valve Closing in Marine Medium-Speed Diesel Engines

In this study,a one-dimensional simulation was performed to evaluate the performance of in-cylinder combustion to control NO_(x) emissions on a four-stroke,six-cylinder marine medium-speed diesel engine.Reducing the combustion temperature is an important in-cylinder measure to decrease NO_(x) emissions of marine diesel engines.The Miller cycle is an effective method used to reduce the maximum combustion temperature in a cylinder and accordingly decrease NO_(x) emissions.Therefore,the authors of this study designed seven different early intake valve closing(EIVC)Miller cycles for the original engine,and analyzed the cycle effects on combustions and emissions in high-load conditions.The results indicate that the temperature in the cylinder was significantly reduced,whereas fuel consumption was almost unchanged.When the IVC was properly advanced,the ignition delay period increased and the premixed combustion accelerated,but the in-cylinder average pressure,temperature and NO_(x) emissions in the cylinder were lower than the original engine.However,closing the intake valve too early led to high fuel consumption.In addition,the NO_(x) emissions,in-cylinder temperature,and heat release rate remarkably increased.Therefore,the optimal timing of the EIVC varied with different loads.The higher the load was,the earlier the best advance angle appeared.Therefore,the Miller cycle is an effective method for in-engine NO_(x) purification and does not entail significant cost.

Effect of Gasoline Property on Formation of Intake Valve and Combustion Chamber Deposits

The cleanliness of gasoline is related to its components and properties.All commercial gasoline builds up deposits on the engine's injector,intake valve and combustion chamber,which can significantly lower the engine performance and influence exhaust gas emissions.In this study,the intake valve deposits (IVD) and combustion chamber deposits (CCD) produced from combustion of fuel containing 21 v%—42 v% of aromatics and 8 v%—31 v% of olefins have been studied using Ford engine tests,and the characteristics of deposits were studied by IR spectroscopy,TGA and elemental analysis instrument.The test results have shown that deposit formation depends on the fuel composition,especially the aromatic content in the fuel.It is also observed that there are differences in the values of IVD and CCD measured by IR spectrometry and elemental analyses.

Experimental Analysis of the Influence of Exhaust Thermal Management on Engine NO_(x) Emission

Exhaust thermal management is essential to allow engines to meet the Euro VI emissions standards and reducing nitrogen oxide emissions is one of the most important targets being pursued nowadays.Along these lines,in the present study,engine’s thermal performances have been evaluated on the basis of a WHTC test,namely a transient engine dynamometer schedule defined by the global technical regulation(GTR)developed by the UN ECE GRPE group(the GTR is covering a world-wide harmonized heavy-duty certification(WHDC)procedure for engine exhaust emissions).The influence of thermal management on fuel consumption,intake,and tailpipe NO_(x) have been quantitatively analyzed for the overrun state.The results have shown that there can be a strong influence on the after-treatment temperatures and tailpipe NO_(x).In particular,the average temperature upstream of the diesel oxidation catalyst(DOC)has been found to increase from 245°C to 254°C,the average temperature of the selective catalytic reduction(SCR)to increase from 248°C to 253°C,the SCR’s minimum temperature to increase from 196°C to 204°C,and the peak value of the NO_(x) emissions in the low-temperature region to decrease from 73 to 51 mg/s.However,the influence of the overrun state’s thermal management strategy on the fuel consumption,the air intake,the ammonia storage,the NO_(2)/NO_(x) ratio,and the urea consumption has been observed to be relatively limited.

Effects of fuel combination and IVO timing on combustion and emissions of a dual-fuel HCCI combustion engine

This paper experimentally and numerically studied the effects of fuel combination and intake valve opening(IVO)timing on combustion and emissions of an n-heptane and gasoline dual-flicl homogeneous charge compression ignition(HCCI)engine.By changing the gasoline fraction(GF)from 0」to 0.5 and the IVO timing from-15°CA ATDC to 35°CA ATDC,the in-cylinder pressure traces,heat release behaviors,and HC and CO emissions were investigated.The results showed that both the increased GF and the retarded IVO timing delay the combustion phasing,lengthen the combustion duration,and decrease the peak heat release rate and the maximum average combustion temperature,whereas the IVO timing has a more obvious influence on combustion than GF.HC and CO emissions are decreased with reduced GF,advanced IVO timing and increased operational load.

Maneuver control at high angle of attack based on real-time optimization of integrated aero-propulsion

To reduce the propulsion system installation thrust loss under high angle of attack maneuvering,a control method based on real-time optimization of the integrated aeropropulsion is proposed.Firstly,based on data fitting and physical principle,an integrated onboard model of propulsion system is established,which can calculate various performance parameters of the propulsion system in real time,and has high accuracy and real-time performance.Secondly,to improve the compatibility of optimization real-time performance and search accuracy,the online optimization control of aero-propulsion system is realized based on an improved trust region algorithm.Finally,by controlling the auxiliary intake valve,a good match between inlet and engine is realized,which solves the problems of intake flow reducing and total pressure recovery coefficient declining,and improves the installation performance of propulsion system.The simulation results indicate that,compared with the conventional independent engine control,the real-time integrated optimization method reduces the installed thrust loss by 3.61%under the design condition,and 4.58%under the off-design condition.Furthermore,the simulation on HIL(Hardware-In-theLoop)platform verifies the real-time performance of integrated optimization method.