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In the present study, detailed comparative experiments on a heavy-duty diesel engine used in the world harmonized transient cycle (WHTC) and road spectrum reversely deduced cycle (RSRDC, which was derived from a road test) were carried out. Fuel consumption and gaseous and particulate pollutants, along with some engine operation parameters, were measured transiently; thus, specific emissions can be calculated. Results showed that the BSFC of WHTC and RSRDC was 201.8 and 210 g/kW·h, respectively, because the real road driving cycle (RSRDC) had wider operating point distributions and more points located in the low-efficiency zone relative to WHTC. Thus, WHTC operations exhibited higher raw CO (abundant CO formation needed a specific temperature threshold) and NOx but lower HC. Furthermore, with aftertreatment, all pollutants met the newest China regulation limit. Finally, transient emissions were analyzed in detail. Although the specific emissions of some pollutants were similar in value for both cycles, transient processes may largely be different. Therefore, the current study is meaningful, and we not only provide broad and detailed information but also directly compare two types of operations (one is a real road driving cycle) in the laboratory: this is rarely discussed in the literature. [ABSTRACT FROM AUTHOR]

In this study, the THC, CO/CO 2 and NOx emissions were investigated by experimental measurements on a twin-spark sporting motorcycle under real-world driving. The emissions at two typical engine steady-state operating points were also added for comparison. Meanwhile, the engine working status was monitored during the whole trip. The results indicate that the small throttle opening and the rich air/fuel ratio make the very low engine combustion efficiency during cold-start phase, which leads to higher THC and CO emissions. During this stage, the CO 2 is also high due to the absolutely high fuel consumption rather than the high combustion efficiency, due to the low NOx emission. By comparing this studied engine to others, the direction to improve the transient response especially under low loads was found. Compared with steady-state operation, both CO and CO 2 during transient driving are lower, because at transient driving the combustion temperature is lower, leading to lower products amounts for those CO precursor (especially for HCO). The lower combustion temperature also leads to lower NOx emission, and the incomplete combustion leads to higher THC emission at cycle driving. In a word, the lower volume efficiency and delay ignition timing result in poorer combustion status during transient driving. • The transient regular emissions of a motorcycle were thoroughly investigated. • The cold start stage contributes large parts of THC and CO, but little of NOx. • The lower CO/CO 2 emissions at transient driving are due to lack of their precursors. • Poor combustion is because of deviation from ideal point of ignition timing and volume efficiency. • NOx is almost only sensitive to the peak in-cylinder temperature during real driving. [ABSTRACT FROM AUTHOR]

• The throttling effects on performances of a heavy-duty diesel engine were explored. • The throttle response of this engine is more sensitive than those in literature. • Exhaust temperature is largely improved after 60 % throttling degree. • Air flow and thermal status were optimized at real driving without much payments. • NOx decreases by ∼43 % after optimizations while fuel consumption is kept unchanged. Heavy duty diesel engines emit over half of mobile source NOx, so SCR is used to reduce NOx. But in applications, SCR is hard to work in desired temperature range. In this work, we try to improve exhaust thermal management and finally reduce NOx through intake throttling effect. Firstly a throttle was designed and its response characteristics were widely explored through steady-state experiment. Results showed that exhaust temperature can be raised largely through intake throttling degree (TD) control, it has obvious effect only after 60 % TD. At 1100 r/min and 65 % TD, exhaust temperature rises by 123.3 °C, 74.2 °C, 49.7 °C and 33.5 °C for 600 N·m, 400 N·m, 200 N·m, and 50 N·m loads, respectively. TD demand for rising transition point becomes larger as engine load decreases, at 600 N·m transition point occurs at 61 % TD, but it increases to 68 % TD at 50 N·m. Finally the intake flow rate was optimized continuously with whole cycle level consideration in transient operation. NOx decreased by 43 % with fuel consumption and HC keeping unchanged, while CO increased by 24.6 %. We hope to provide a good example for diesel engine performance improvement from optimization of existing technologies without too much cost. [ABSTRACT FROM AUTHOR]

In this work, the effect of ignition modes on engine performance is discussed in detail. Torque, ECR (energy consumption rate), emissions and knock are investigated by using combining experiment with CFD (computational fluid dynamics). The results are as following: the torque of synchronous twin-spark is more excellent (for example, the torque improves by 2.3% under 60% engine load and 5000 rpm) relative to single-spark or the asynchronous ignition mode of twin-spark; the synchronous twin-spark ignition mode has shorter combustion period and less heat transfer loss, resulting in the lower ECR (under 60% engine load and 5000 rpm, it decreases by 3.7%).; unexpectedly all the emissions of synchronous twin-spark are higher (increased by 12%, 53.1% and 9.4% for HC, CO and NOx, respectively under 60% engine load, 5000 rpm) than those of single-spark. Then, we used CFD to reveal the seemingly contradictory phenomenon. And found that, under synchronous twin-spark mode, due to the specifically interaction form between flame and turbulence, the maximum in-cylinder temperature is higher and it decreases faster. This results in specifically pollutants formation patterns. The investigation provides a deeply understanding of in-cylinder working process under multi-ignition, and gives us a foundation for the optimization of ignition modes. • Performances of a twin-spark motorcycle engine were studied over a wide range condition. • Synchronous twin-spark ignition gives the best performances except emissions. • All emissions (HC, CO and NOx) are higher under Synchronous twin-spark ignition. • The unexpected emission behaviors were explored by CFD. • The interaction between flame front and turbulence was revealed through CFD. [ABSTRACT FROM AUTHOR]

• Chemical mechanism was introduced to study λ 's effect on natural gas-diesel engine. • Each combustion stage of natural gas-diesel engine was quantitatively analyzed. • The higher λ leads the heat release rate to shoot up earlier. • The 10–50% and 50–90% combustion duration become longer as λ increases from 1.2. • The maximum nitrogen oxide emissions appear near the λ of 1.1. In the presented study, the influence of lean-burn on combustion and emission performance of diesel pilot ignition natural gas engine was investigated by using the method of computational fluid dynamics coupling with the reduced chemical kinetic model. Based on bench tested results, the computational fluid dynamics model was validated in four typical conditions, and then it was used for the simulation at different excess air coefficient. Due to the visibility of computational fluid dynamics results, the combustion medium process and emissions medium products were obtained, which then were used to explain the influence mechanism of excess air coefficient. The simulated results show that, under 50% load, the maximum cylinder pressure becomes larger and the start of combustion is advanced when the excess air coefficient increases from 1.0 to 1.5, and the maximum advance of the start of combustion reaches 9.5 °CA. Nevertheless, under 100% load, the start of combustion is advanced first and then retarded. Meanwhile, the higher the excess air coefficient is, the earlier the heat release rate shoots up. When the excess air coefficient increases from 1.2, the 10–50%, 50–90% and 10–90% combustion duration become longer. The nitrogen oxide emission increases as the excess air coefficient rises from 1.0 to 1.1 but decreases if it continues to increase. The unburned methane emission decreases first and then increases with the increase of the excess air coefficient. Nevertheless, at 1500 rpm and full load, the unburned methane emission shoots up as the excess air coefficient changes from 1.3 to 1.5 and the maximum difference of unburned methane emission reaches 3233 ppm. [ABSTRACT FROM AUTHOR]

Highlights • Chemical kinetic mechanism was introduced to study the combustion and emissions of NG-diesel engine. • The influence of spray angle on each combustion stage of NG-diesel engine was quantitatively analyzed. • The maximum output power of NG-diesel engine appears near the spray angle of 140°. • Combustion duration becomes longer as spray angle increases from 60° to 100° at 1000 rpm and 50% load. • CH 4 emissions at 1000 rpm and 100% load are almost unchangeable with the change of spray angle. Abstract In this research, the computational fluid dynamics (CFD) coupled with reduced chemical kinetic model was applied to study the combustion process and emissions characteristics of a NG-diesel dual fuel engine at various injector spray angles. The model was validated by measured data of in-cylinder pressure, heat release rate (HRR) and emissions (nitrogen oxide (NOx), hydrocarbons (HC), carbon monoxide (CO)) in the NG-diesel dual fuel engine. The validated CFD models were used to investigate the immediate process of combustion and emissions of NG-diesel dual fuel engine with the variation of spray angle. The results showed that the peak cylinder pressure increases as the spray angle increases from 60° to 140°, but slightly decreases if the spray angle continues to increase to 160°. Except for the condition of 1000 rpm and 50% load, the start of combustion (SOC), CA50, 10–50% combustion duration, CA90, 50–90% combustion duration and 10–90% combustion duration decrease as the spray angle increases from 60° to 120°, and keep minor fluctuations when the spray angle increases from 120° to 160°. The NOx emissions ascend when the spray angle increases from 60° to 140° and changes little if it continues to increase from 140° to 160°. Nevertheless, the unburned methane is almost unchangeable at 1000 rpm and 100% load. When the spray angle ranges between 120° and 160°, the CO emissions keep at a lower level. All these have provided visual data and theoretical guidance for improving the combustion and emissions performance of NG-diesel dual fuel engine. [ABSTRACT FROM AUTHOR]

[Display omitted] • The purification efficiency characteristics and interactions of each catalyst in the integrated aftertreatment system are revealed. • CO and HC basically achieve almost 0 when the DOC temperature is higher than 600 K. • The NO reaction rate is closely related to DOC temperature. • Inlet pressure of DOC has almost no effect on the conversion of HC and CO. • When the temperature is higher than 500 K, the NOx conversion efficiency of SCR is very high. In this paper, the emission characteristics and catalytic reactors interactions of a non-road diesel engine are investigated under non-road transient cycle (NRTC) by experiment and system level simulation. The results showed that the overall emission conversion efficiency of hydrocarbon (HC), carbon monoxide (CO), nitrogen oxides (NO X) and particulate matter (PM) is 96.68 %, 91.45 %, 97.67 % and 93.33 %, respectively under NRTC in experiment. In addition, the interactions of each catalytic converter for emissions under NRTC have been obtained through simulation. When the diesel oxidation catalytic (DOC) temperature is higher than 600 K, CO and HC emissions basically achieve almost 0 through DOC purification. Furthermore, DOC can convert nitric oxide (NO) into nitrogen dioxide (NO 2) which provides strong oxidation for the passive regeneration of diesel particulate filter (DPF). The NO reaction rate is closely related to DOC temperature. And the average conversion efficiency from NO to NO 2 in DOC is 40.36 %. Moreover, the DOC inlet pressure has almost no effect on the conversion of HC and CO. When the temperature of selective catalytic reduction (SCR) is higher than 500 K, the averages NOx conversion efficiency of SCR is up to 98.74 %. And ammonia purification catalyst (ASC) can further reduce NO emissions while absorbing slip ammonia. When the inlet temperature of DPF is more than 520 K, it has almost no effect on the oxidation of PM. The PM conversion efficiency of aftertreatment system (ATS) is mainly affected by the PM collection efficiency of DPF. The average PM collection efficiency of DPF is 53.32 %, while the PM conversion efficiency of ATS is 91.54 % by simulation. Although DPF will convert PM to CO, these CO cannot be completely converted into carbon dioxide (CO 2). So the CO conversion efficiency of ATS is lower than that of DOC. [ABSTRACT FROM AUTHOR]

In this paper, experimental studies were conducted on a single cylinder high speed spark ignition (SI) motorcycle engine under both full load and partial load at 6500 and 8500 rpm with pure gasoline, 30% and 35% volume butanol-gasoline blends. This study is trying to find out the influence on combustion heat release of high speed SI engine by variables including ignition timing, butanol blend ratio and engine load. The results show that butanol-gasoline blend provides higher knocking resistance by allowing advance ignition timing in SI engines, which leads to more efficient combustion. With butanol blend ratio increases, more complete combustion process will achieve with the optimum operating parameters. With engine load increases, the rates of heat release become faster and ascend in peak value for both pure gasoline and butanol-gasoline blends. Furthermore, engine performance parameters such as power, fuel economy and emissions have been compared and analyzed. The results also show that engine power, torque, brake specific energy consumption, HC, CO and O 2 emissions are better than those of pure gasoline at full load with 35% volume butanol addition, combined with ignition timing optimization. But NOx and CO 2 emissions are higher than those of the original level of pure gasoline. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ignition timing has been optimized. [•] 1% H2O has been added. [•] Positive results have been achieved in engine torque, BSEC, CO emissions and HC emissions. [•] NOx and CO2 emissions go up. [ABSTRACT FROM AUTHOR]

In this study, the single-spark natural gas (NG) SI engine was simulated by using the CFD coupled with detailed combustion mechanism, and validated against with the experiment data. Additionally, the axisymmetrically twin-spark plugs were placed diametrically opposite to each other in the combustion head of the NG SI engine, and fired simultaneously during the simulation cases to trigger two independent spark kernels. The results indicated that twin-spark plugs yielded approximate combustion phasing and better fuel conversion efficiency. Interestingly, in the early stages of flame propagation triggered by the twin-spark plugs configuration, two independent spark kernels looked remarkably similar to the iconic of "Taiji" diagram of the Chinese Taoism, and two independent flame kernels were obviously moved along with the flow. The strong flow pushed the flame front close to the side of the intake port of the NG SI engine equipped with the single-spark plug. While two independent flame fronts of the NG SI engine equipped with the twin-spark plugs were located separately at the intake and exhaust ports in the combustion chamber. Furthermore, two independent flame fronts mutually collided with each other, and generated more independent combustion block areas in the center of the combustion chamber. • The full-size 3D model of lean-burn SI natural gas engine equipped with the twin-spark plugs was simulated. • Two independent spark kernels looked similar to the iconic of "Taiji" diagram of the Chinese Taoism. • Two independent flame fronts mutually collided and generated more independent combustion block areas. [ABSTRACT FROM AUTHOR]

• The impact of IVC timing on the performance of DPI NG engine was analyzed. • The IVC timing has evident influence on the volumetric efficiency. • The in-cylinder turbulence kinetic energy decreases as the IVC timing is later. • IVC timing strategy has little effect on HC and CO emissions. • The NOx emissions decrease with the retarding of IVC timing. In the present study, a diesel engine was modified to a diesel pilot ignited natural gas engine and the influences of intake valve closing timing on in-cylinder flow, combustion and emission performance of engine were investigated by three-dimensional computational fluid dynamics simulation. Based on the geometric model and basic parameters of this engine, the simulation model was built under three operating conditions and then validated by experimental data. On this basis, the validated model was applied to investigate the effects of the intake valve closing timing strategy. The simulation results indicated that, the volumetric efficiency decreases with the retarding of intake valve closing timing in three cases while it increases as the intake valve closing timing is advanced by 10°CA at 1200 rpm. The in-cylinder turbulence kinetic energy decreases with the retarding of intake valve closing timing. The peak in-cylinder pressure decreases when the intake valve closing timing is either advanced or retarded at 50% load. Nevertheless, the maximum peak in-cylinder pressure occurs at advancing 10°CA intake valve closing timing at 1200 rpm and 100% load, which rises by 4.5 bar compared with that at the original intake valve closing timing. Additionally, the maximum heat release rate appears at advancing 10°CA intake valve closing timing at 100% load, which is 26 J/deg higher than that at the original intake valve closing timing. Simultaneously, the shortest combustion duration occurs at advancing 10°CA intake valve closing timing at 1200 rpm and 100% load. For the emissions, the NOx emissions decrease with the retarding of intake valve closing timing but the variation becomes unobvious with the advancing of the intake valve closing timing. Besides, the intake valve closing timing strategy has little effect on HC and CO emissions. [ABSTRACT FROM AUTHOR]