Ahyun Ko

Experimental study of particle emission characteristics of a heavy-duty diesel engine and effects of after-treatment systems: Selective catalytic reduction, diesel particulate filter, and diesel particulate and NOx reduction

This investigation focused on the particle emission characteristics of a heavy-duty diesel engine and the effects of after-treatment systems such as diesel particulate filter and selective catalytic reduction. The test engine was operated on the worldwide harmonized transient cycle mode, which is a new transient cycle for Euro 6, and the conventional European transient cycle mode. Four combinations of after-treatment systems, engine-out, selective catalytic reduction, diesel particulate filter, and diesel particulate and nitrogen oxide reduction, were evaluated for the transient cycles, respectively. The whole test procedure, as part of the Korea particulate measurement programme and the inter laboratory correlation exercise for domestic heavy-duty diesel engines, complied with the recommended method of particulate measurement programme. The particles that were extracted through the golden particle measurement system the constant volume sampler tunnel consisted of solid particles like carbonaceous fraction, metal ash, etc. The particles emitted from the tail-pipe, as analyzed by the differential mobility spectrometer, included volatile or soluble particles like sulphate fraction, nitrate fraction, and organic fraction. The test results showed that the particle number and size distribution depended on the catalytic activity or filtration efficiency of the after-treatment system. Compared to the accumulation mode, the nucleation mode was easily caught or oxidized by the after-treatment system. Additionally, the nucleation mode was sharply increased by excessive ammonia injection because nitrogen dioxide-assisted diesel particulate filter regeneration resulted in reduced conversion efficiency of the selective catalytic reduction.

Study of regulated emissions and nanoparticle characteristics of light-duty direct-injection vehicles fuelled with gasoline and liquefied petroleum gas in the New European Driving Cycle and the Federal Test Procedure 75 driving cycle

This study evaluated the pollutants and nanoparticles, the fuel economy and the levels of carbon dioxide emissions of vehicles equipped with a 1.6 l direct-injection spark ignition engine fuelled by gasoline or by liquefied petroleum gas. The nanoparticles were analysed using a particle measurement system that is used in Europe for regulatory purposes. A fast-response particle size and number spectrometer (model DMS500) were used to characterize the size-resolved particle distributions. The vehicle was tested on a chassis dynamometer for the New European Driving Cycle and Federal Test Procedure 75 in its factory default state (gasoline version) and modified state (for liquefied petroleum gas fuel), and the results were compared. The liquefied-petroleum-gas direct-injection vehicle emitted significantly lower levels of total hydrocarbons than did the gasoline direct-injection vehicle. However, the levels of nitrogen oxide emissions from the liquefied-petroleum-gas direct-injection vehicle were equivalent to those from the gasoline direct-injection vehicle. Because of the higher combustion and exhaust temperatures and relatively higher loads imposed during the driving cycles, the liquefied-petroleum-gas direct-injection vehicle showed a slightly higher level of nitrogen oxide emissions. The particle emissions from the vehicles were mainly affected by the vehicle driving conditions of the test driving cycles. In particular, the particle emissions from the vehicle were pronounced in the cold-start and accelerating phases of the emission certification standards. The nanoparticles from the liquefied-petroleum-gas direct-injection vehicle were significantly fewer in number, exhibiting a reduction of over 99%.

Effect of EGR Rate and Injection Timing on the Characteristics of Exhaust Emissions in Light-duty Diesel Engine

Abstract : Cooled EGR system is widely used to reduce NOx emissions in diesel engine. But when EGR rate was increased, combustion stability was worsened and PM level was increased. So determining optimized control point of EGR rate is important. In order to determine this point, it is important to figure out the effect of EGR system on the exhaust emissions. In this research, NOx and PM emissions were analyzed with various coolant temperature supplied to the EGR cooler at several positions such as downstream of turbocharger, upstream and downstream of DPF. Effects of some variables such as EGR rate, hot / cooled EGR and change of injection timing were estimated. And CO 2 emissions were measured at exhaust and intake manifold to calculate EGR rate at each engine operating condition. Also combustion analysis was performed in each engine operating conditions. In the result of this study, there was trade-off between NOx emissions and PM emissions. When EGR rate was increased, combustion pressure was decreased and COV of IMEP was increased.

A Study on NOx Reduction Characteristics of LNT Catalyst with Fuel Injection Control in Light-duty Diesel Engine

Lean NOx Trap (LNT) catalysts are capable of reducing exhaust NOx emissions from diesel engines. LNT stores NOx in lean condition and exhausts N2 by reducing NOx in rich condition. NOx reduction characteristic of LNT catalysts using throttle position sensor and fuel injection timing control for light-duty diesel engine was investigated. In contrast to SCR system, LNT catalyst uses diesel fuel in resuctant. Also if the concentration of reductant is exceeded, excessive amount of reductant will slip throughout LNT and cause another emission problem. Thus LNT regeneration with precise engine control established that can make higher NOx conversion efficiency and lower fuel penalty, prevent another emission problem. NOx and reductant concentration were measured by the NOx sensor and Mexa7100D equipped inlet and outlet of catalyst. As a result of engine test, regeneration strategy has reached high of 77.8% NOx conversion efficiency according to engine operation condition. Moreover, we have proved that it is possible to use regeneration strategy of LNT within 5% fuel penalty.

Study of Particle Emission Contour Construction & Characteristics and Reduction Efficiency of Exhaust-Treatment System of Diesel Engine

Key Words: PM(입자상물질), DPF(매연여과장치), EGR(배기재순환), DMS(고속입자상물질측정장치),NucleationMode(핵화모드),AccumulationMode(축적모드)초록: 본연구는승용디젤엔진의입자상물질배출특성에관한것으로써, 엔진에서배출된입자상물질이배기관및후처리장치인디젤산화촉매와매연여과장치를통과할때의특성변화를파악하기위하여후처리장치각각전 후단및배기관에서직접측정하였다.또한다양한엔진회전속도및부하조건에서측정함으로써입자상물질배출맵을구축하였으며,디젤산화촉매및매연여과장치의입자상물질저감효과에대해평가하였다.뿐만아니라배기재순환율과연료분사시기를변경시켜입자상물질의배출특성변화를파악하였다.모든시험에서입자상물질을5~1000nm크기까지측정할수있는DMS500을이용하였다.Abstract: Inthisstudy,wemainlyfocusedonthePM(ParticulateMatter)emissioncharacteristicsofadieselengine.To analyze particle behavior in the tail-pipe, particle emission was measured on the engine-out (downstream ofturbocharger), each upstream and downstream both of DOC (Diesel Oxidation Catalyst) and DPF (Diesel ParticulateFilter). Moreover, particle emission contours on each sampling point were constructed. The reduction efficiency ofparticlenumberconcentrationandmassthroughtheDOCandDPFwasstudied.ParameterssuchasEGR(ExhaustGasRecirculation) and the main injection timing were varied in part load conditions and evaluated using the engine-outemissions. TheDMS500(Differential MobilitySpectrometer) wasusedasaparticlemeasurement instrument that canmeasure particle concentrations from5 nmto 1000 nm. Nano-particles of sizes less than 30 nmwere reduced byoxidationorcoagulatedwithsolidparticlesinthetail-pipeandDOC.TheDPFhasaveryhighfiltrationefficiencyoveralloperatingconditionsexceptduringnaturalregenerationofDPF.

Experimental Evaluation of EGR and Fuel Injection Pressure on Combustion, Size-resolved Nano-particle and NOx Emissions Characteristics in an Advanced Light-duty Diesel Engine

Abstract : In order to satisfy stringent future emission regulation in diesel engines, systematic approaches to mitigate the harmful exhaust emissions were developed, such as engine hardware, fuel injection equipment, engine control, and after-treatment system. In this study, to improve the nano-particle and NOx emissions from a state-of-the-arts diesel engine, effect of various EGR and fuel injection pressure with combustion analysis were evaluated. Size-resolved nano-particle and NOx emissions showed trade-off characteristics with various EGR rate and increment of fuel injection pressure. Key words :EGR(배기재순환), NOx(질소산화물), Nano-particle(입자상물질), Fuel injection pressure(연료분사압력), Diesel engine(디젤엔진) Nomenclature 1) IMEP : indicated mean effective pressure, barBMEP : brake mean effective pressure, barMBF : mass burned fraction, % 1. 서 론 자동차에서 배출되는 배기가스는 대기오염의 주요한 원인으로써, 세계적으로 자동차에서 배출되는 배기가스 규제를 점점 강화하는 추세이다. 자동차에서 배출되는 질소 산화물 및 입자상 물질은 중추 신경 및 호흡기를 자극하고 산성비 및 대기 중에서 * Corresponding author, E-mail: spark@korea.ac.kr