基于轻型柴油机台架试验平台,研究柴油机氧化型催化转化器(DOC)载体长度变化对后处理系统减排性能的影响.结果表明:适当增大DOC载体长度可提高对一氧化碳(CO)、总碳氢化合物(THC)和一氧化氮(NO)的氧化率,过量增大对氧化性能的提升有限,同时影响DOC在低温低负荷下减排效果;DOC耦合催化型柴油机颗粒捕集器(CDPF)对颗粒物数量(PN)的减排效果受DOC载体长度影响较小.从兼顾成本与性能的角度出发,适当增大DOC载体长度能有效提高减排效果,但过量增大对减排效果提升影响不大.

Diesel engines are used extensively due to their superior economy and strong power performance, but the air pollution these engines produced is hard to overlook. With regulatory legislations for diesel engine emissions becoming stricter worldwide, integrated after-treatment systems are becoming increasingly important. The reduction performance of after-treatment systems can be affected by many factors. In this study, we investigated the effects of diesel oxidation catalytic converter (DOC) catalyst composition on gaseous emissions characteristics for the after-treatment systems. The after-treatment systems consisted of a diesel oxidation catalytic converter (DOC), a catalyzed diesel particulate filter (CDPF), and a selective catalytic reduction (SCR). An engine dynamometer test was conducted on a light-duty diesel engine which equipped with DOC + CDPF + SCR systems. All DOCs used were coated with Pt-Pd catalyst material. The experiment was performed under steady-state conditions of Yunnei D20TCI diesel engine with a displacement of 1.9 liters. This experiment used four sampling points located between the front and rear ends of each after-treatment device. During the full-load test, the data were collected every 200 revolutions from 1 000 to 3 200 r/min. The partial load test was conducted at the maximum torque speed (2000 r/min) with five loads: 10%, 25%, 50%, 75% and 100%. During the test, the data of different Precious Group Metal (PGM) load and Pt/Pd ratio of DOC were collected. Five sets of DOC catalyst composition were used: 2120 (Pt/Pd, 5:1), 1410 (5:1), 880 (5:1), 880 (7:1), 880 (10:1) g/m3. The results showed that the light-off temperatures (T50) of carbon monoxide (CO) and total hydrocarbon compounds (THC) elevate with the decrease of PGM load. And the T50of CO and THC both increased with the growth of Pt/Pd ratio. No significant gap existed between the various DOC catalyst composition, indicating that the Pt/Pd ratio of DOC had little influence on the engine's economic performance. The CO oxidation activities increased monotonically as the PGM load, or Pt/Pd ratio increased in a low-temperature range (< 300 ℃), but this beneficial effect mitigated as the temperature was enhanced continuously (≥ 300 ℃). The trends of oxidation activity of THC were similar to CO. Nitric oxide (NO) oxidation was enhanced with higher PGM load. NO oxidation activity was more sensitive to Pt element which can amplify it, exhibiting an opposite trend to CO and THC. But the maximum NO conversion did not reach 50% for all DOCs. High temperature was adverse to NO reaction since it was exothermic. When the SCR inlet temperature was low, high nitrogen dioxide (NO2) concentration can increase the SCR nitrogen oxides (NOx) reduction. NOxreduction was above 90% without large gap when the SCR inlet temperature is high. Along with the flow direction, the average temperature drop in the SCR was the largest, followed by the DOC. The average NO2/NOxratio increased by 23.9% through the DOC. DOC pressure drop was about 1.4 kPa, and DOC pressure drop at CDPF was about 4.1 kPa. Besides, no significant influence of DOC catalyst composition of CDPF pressure drop under full load was found.

Based on a diesel bus certified to ChinaIIIemission standards, thecomposition of particulates emission with different proportions of biodiesel was investigated during China city bus cycle (CCBC) on a heavy chassis dynamometer. The results show that soluble organic fraction (SOF) was mainly consists of fatty acid and N-alkanes, while Hopanes and PAHs account for less than 7%. Biodiesel has a significant impact on the compositions, with the proportion of biodiesel going up, EC decreased while OC/EC and SOF increased, C18:2 and C18:1 of fatty acids increased apparently while C12:0 and C14 decreased, N-alkanes and Hopanes components also decreased. The mass of PAHs is concentrated in medium and small molecular with 3 or 4 Benzene rings, while the toxicity of PAHs concentrated in medium and high molecular with more than 4 Benzene rings. When using biodiesel, the mass of PAHs decreased apparently, especially Pyr, FL and PA, while the toxicity changedlittle.

Nowadays, the performances of diesel engines under transient conditions become the research focus. Because of the frequent start and stop of the series hybrid diesel engine, the diesel engine is always in the steady state or idle speed switching state. In order to study the transient performance of diesel engine during the idle transient conditions, 3 indices are firstly adopted: The lag coefficient, which is an evaluation index for performance of diesel engine transient lag, the deterioration coefficient, which is an evaluation index for performance of diesel engine transient deterioration, and the transient mean, which is an evaluation index for comprehensive performance of diesel engine transient process. And then an analysis is carried out from the 3 dimensions of time, peak and mean value, and the influences of idle transient transition time and injection parameters on the maximum cylinder pressure, fuel flow and emissions are investigated. The test results show that the cylinder pressure, fuel consumption and emission performance of the diesel engine are worse than the steady state during the transient conditions. The deterioration of the engine can be reduced in the idle speed transient process by adjusting the transition time and smoke emission limit. With the increase of the transition time, the transient mean and lag coefficient of the maximum cylinder pressure decrease, and the deterioration coefficient increases; with the smoke limit increasing, the lag coefficient of the maximum cylinder pressure increases, and the deterioration coefficient and transient mean decrease. When the transition time is 10 s and the smoke emission limit is reduced by 10%, the lag coefficient of the maximum cylinder pressure gets the minimum value of 0.7. When the transition time is 3 s, and the smoke emission limit increases by 10%, the deterioration coefficient obtains the minimum value of 0.69. When the transition time is 10 s, and the smoke emission limit increases by 10%, the transient mean of the maximum cylinder pressure takes the minimum value of 5.79 MPa. With the increase of the transition time, the lag coefficient, deterioration coefficient and transient mean of fuel flow first increase and then decrease; with the increase of smoke emission limit, the lag coefficient and deterioration coefficient of fuel flow increase, and the transient mean decreases. When the transition time is 10 s, and the smoke emission limit is reduced by 10%, the lag coefficient of fuel flow gets the minimum value of 1.1. When the transition time is 3 s, and the smoke emission limit increases by 10%, the deterioration coefficient obtains the minimum value of 1.01. When the transition time is 10 s, and the smoke emission limit is increased by 10%, the fuel flow gets the minimum value of 12.49 kg/h. With the increase of the transition time, the lag coefficient and the transient mean of NOx emission decrease, and the deterioration coefficient increases; with the smoke emission limit increasing, the lag coefficient and the deterioration coefficient of NOx emission increase, and the transient mean decreases. When the transition time is 10 s, and the smoke emission limit is reduced by 10%, the lag coefficient of NOx emission gets the minimum value of 1.1. When the transition time is 5 s, and the smoke emission limit is reduced by 10%, the deterioration coefficient obtains the minimum value of 1.046. When the transition time is 10 s, and the smoke emission limit is invariable, the transient mean of NOx emission takes the minimum value of 7.23×10-4. With the increase of the transition time, the lag coefficient of smoke emission first increases and then decreases, and the deterioration coefficient and transient mean increase; with the smoke emission limit increasing, the lag coefficient of smoke emission increases, and the deterioration coefficient and transient mean decrease. When the transit time is 10 s, and the smoke emission limit is reduced by 10%, the lag factor of smoke emission obtains the minimum value of 0.7. When the transition time is 3 s, and the smoke emission limit increases by 10%, the deterioration coefficient obtains the minimum value of 5.2. When the transition time is 3 s, and the smoke emission limit is increased by 10%, the transient mean of smoke emission takes the minimum value of 0.025 m-1. These 3 indices can be used to evaluate the performance of the diesel engine in the transient process, which can provide the basis for further optimization.