| 摘要: | 本研究係針對不同車用柴油品質參數對車用柴油引擎有害空氣污染物排放之影響，以標準柴油引擎架設於動力計上以三種不同引擎運轉模式，測試十六烷值及添加不同芳香烴種類含量之柴油，分析其排氣中傳統性空氣污染物(PM、CO/CO2、NOx及HC等)之排放係數及多環芳香烴化合物(Polycyclic Aromatic Hydrocarbons,PAHs)之排放特徵。
車用標準柴油引擎設計在三種不同引擎運轉模式下，添加不同比例之二環及三環芳香烴添加劑於市售柴油中作為測試燃料，以研究柴油引擎廢氣排放之影響及變化趨勢。以氣相層析質譜儀(GC/MS)分析測試柴油及柴油引擎排放廢氣中之二十一種多環芳香烴化合物之含量、濃度，及利用引擎操作參數進一步取得之PAHs排放係數。本研究所得之結論歸納如下：1.柴油油品中總PAH含量以及總BaPeq 分別為227以及1.24 mg/L其中低環數之PAHs佔總量之97.1% 。2. 三種引擎運轉模式中以高速公路行駛模式下重柴油引擎排放之PAH總濃度最低(373 μg/Nm3)，其次為市郊模式(602 μg/Nm3)、市區運轉模式(1130 μg/Nm3)，三種模式之權重濃度為702 μg/Nm3。3.市售柴油添加不同比例二環芳香烴添加劑（D1及D2）對柴油引擎排放總PAHs濃度分別為876 μg/Nm3 、1470 μg/Nm3為市售柴油（DB）之1.25以及2.09倍，其中Nap佔總排放濃度44.0%及44.7%。市售柴油添加不同比例三環芳香烴添加劑（D3及D4）對柴油引擎排放總PAHs濃度分別為 1150 μg/Nm3 、 1380 μg/Nm3為DB之1.64以及1.96倍，其中Acp佔總排放濃度14.7%及33.4%，皆顯示顯示其影子效應(Shadow effect)相當明顯，其中三環添加劑對高環數之PAHs除FL、Pyr、BeP、BaP、BbC外，均顯示出增加生成之機會並殘存於排氣煙道中。4.市售柴油引擎測試後，耗用每公升柴油PAHs之平均排放係數為14500 mg/L-fuel，而D1、D2、D3、D4引擎之PAHs權重排放係數分別為15600 mg/L-fuel、33200 mg/L-fuel、26200 mg/L-fuel以及30500 mg/L-fuel，均顯示在市區行駛條件下排放係數最高。5. 三種引擎運轉模式中其PAHs排放率介於2000～2700 mg/min之間，其權重為2300 mg/min，添加三環芳香烴添加劑對高環數PAHs排放率有增加之趨勢。6.市售柴油引擎之PAHs O/I值平均為0.06，在五種測試用油中之PAHs O/I值均在柴油引擎燃燒反應中均大量被破壞分解，但對於個別之PAH並無一致之生成或削減現象。
Diesel vehicle emissions are a major source of air pollutants as NOx, SOx, HC, CO, PM, and air toxics those play important roles in ambient air quality. One of the strategy reducing air pollutants from diesel vehicles was to limit or improve the compositions, criterions in fuels. In Diesel fuel, the four important relative principles and regulations are to assess the air quality effect of vehicle diesel fuel specifications from heavy-duty diesel engine including Cetane index (CI), sulfur content, poly-aromatic content and total aromatic content. However, the diesel specifications only set the criteria limitation of Cetane index and sulfur content in Taiwan. After 2007, total aromatic content will be also restricted by Taiwan EPA.
In this study, Polycyclic aromatic hydrocarbons (PAHs) emission test for a heavy-duty diesel (HDD) engine was simulated to operate under 3 steady-state cruising modes by a DC-current dynamometer with fully automatic control system and fueled, respectively, with commercial diesel fuel and blend with different batch fractions of two poly-aromatic hydrocarbon additives, Naphthalene and Acenaphthene. PAH in tailpipe gas and particulate samples from the dilution tunnel were collected by using a PAH sampling system. Twenty one individual PAHs were analyzed primarily by a gas chromatography with mass spectrometer (GC/MS). Also, the traditional air pollutants including PM、CO/CO2、NOx were simultaneously analyzed on line, separately.
The results of this study were summarized as follows.
1. The mean total-PAH and its BaPeq content in diesel fuel was 227 and 1.24 mg/L, 2- and 3-rings PAHs content fraction was more than 97.1%
2. In the exhaust of HDD fueled commercial diesel (DB), total PAH emission weighting concentration was 702 μg/Nm3. The highest PAH emission concentration was 1130 μg/Nm3 under urban driving mode, the other concentrations were 602 and 373 μg/Nm3, respectively, rural and highway driving modes.
3. For HDD engine fueled by adding 1% and 3% Nap respectively, the total PAHs emission weighting concentrations were 876 and 1470 μg/Nm3, those were 1.25、2.09 times higher than fueled DB. By adding 1% and 3% Acp, the total PAHs emission weighting concentrations were 1150 and 1380 μg/Nm3, those were 1.64、1.96 times higher than fueled DB.
4. The total-PAHs emission factor (mg/L-fuel) of HDD engine fueled by 5 five target diesel fuel were respectively 14.5 (DB), 15.6 (DB+1% Nap), 33.2 (DB+3% Nap), 26.2 (DB+1% Acp) and 30.5 mg/L-fuel (DB+3% Acp). The highest emission factors were found under urban mode by those 5 HDD engines.
5. The HDD engine had high total-PAH emission rate, which were between 2000~2700 μg/min, and mean emission rate was 2300 μg/min. Blending 2- and 3-ring aromatic additives will raise up the total-PAH emission rate under three cruising modes.
6. The results of Output/Input ratio of PAH mass for HDD engines were 0.06 fueled by commercial diesel fuel. In five target diesel fuels, most PAHs are with depletion process in HDD engines, however, few PAHs are not the same process. |
