衛(wèi)海橋,王?楠,李?衛(wèi),賈德民,李金光,潘家營
進(jìn)氣道噴射氫發(fā)動(dòng)機(jī)燃燒及爆震特性試驗(yàn)研究
衛(wèi)海橋1,王?楠1,李?衛(wèi)2,賈德民2,李金光1,潘家營1
(1. 天津大學(xué)內(nèi)燃機(jī)燃燒學(xué)國家重點(diǎn)實(shí)驗(yàn)室,天津 300072;2. 濰柴動(dòng)力股份有限公司,濰坊 261041)
為探究進(jìn)氣道噴射(PFI)氫發(fā)動(dòng)機(jī)燃燒特性,以一臺(tái)四沖程PFI氫發(fā)動(dòng)機(jī)為研究對象,開展了關(guān)鍵參數(shù)(點(diǎn)火時(shí)刻、當(dāng)量比)對氫發(fā)動(dòng)機(jī)燃燒及爆震特性影響的試驗(yàn)研究,其中點(diǎn)火時(shí)刻在-5°CA~-30°CA內(nèi)變化,當(dāng)量比在0.5~0.8內(nèi)變化.結(jié)果表明,隨著點(diǎn)火時(shí)刻從-5°CA提前到-30°CA,發(fā)動(dòng)機(jī)做功能力逐漸降低,循環(huán)變動(dòng)逐漸增大;將當(dāng)量比從0.5提高到0.7時(shí),發(fā)動(dòng)機(jī)做功能力有所下降且循環(huán)變動(dòng)增大,綜合發(fā)動(dòng)機(jī)做功能力和循環(huán)變動(dòng)來看,-15°CA點(diǎn)火時(shí)刻發(fā)動(dòng)機(jī)性能最優(yōu);根據(jù)統(tǒng)計(jì)學(xué)角度分析得知,從點(diǎn)火時(shí)刻-25°CA開始,隨著點(diǎn)火時(shí)刻的推遲,平均爆震強(qiáng)度呈現(xiàn)先增大后降低的趨勢;平均爆震強(qiáng)度隨當(dāng)量比的提高整體呈增大趨勢,但其對當(dāng)量比的敏感性與點(diǎn)火時(shí)刻密切關(guān)聯(lián),-15°CA~-20°CA點(diǎn)火時(shí),增大當(dāng)量比會(huì)使平均爆震強(qiáng)度明顯增加;同時(shí),點(diǎn)火時(shí)刻較為提前或推遲時(shí)爆震概率對當(dāng)量比的敏感性較大,增大當(dāng)量比會(huì)使爆震概率明顯增加、爆震起始時(shí)刻提前.此外,在高當(dāng)量比條件下,初期循環(huán)中一般強(qiáng)度爆震的累加作用會(huì)誘發(fā)超級爆震.
氫發(fā)動(dòng)機(jī);燃燒特性;爆震;超級爆震;點(diǎn)火時(shí)刻;當(dāng)量比
日益減少的原油儲(chǔ)備和愈發(fā)嚴(yán)重的環(huán)境污染迫使研究學(xué)者一直致力于尋找高效、清潔、可再生的替代燃料[1-2].氫氣作為一種發(fā)動(dòng)機(jī)燃料,具有很多優(yōu)點(diǎn),比如氫氣可由可再生能源制取,完全燃燒時(shí)產(chǎn)物只有水,可以實(shí)現(xiàn)全生命周期的零碳排放[3].氫氣質(zhì)量能量密度高,擁有較寬的可燃界限、最小的點(diǎn)火能量以及較快的火焰?zhèn)鞑ニ俣萚4].根據(jù)奧托循環(huán)理論,其較快的火焰?zhèn)鞑ニ俣瓤梢詫?shí)現(xiàn)更高的熱效率[5].但氫氣也存在局限性,如體積熱值低、NO排放高,容易引起早燃、回火、爆震等異常燃燒現(xiàn)象[6],不僅會(huì)降低發(fā)動(dòng)機(jī)的功率輸出,嚴(yán)重時(shí)會(huì)導(dǎo)致發(fā)動(dòng)機(jī)部件的不可逆損壞[7-9].
進(jìn)氣道噴射式(PFI)氫發(fā)動(dòng)機(jī)由于其裝置簡單且耐久性好等優(yōu)點(diǎn)受到廣大研究人員的重視,但是PFI氫發(fā)動(dòng)機(jī)的異常燃燒現(xiàn)象也更為嚴(yán)重.研究人員為深入理解PFI氫發(fā)動(dòng)機(jī)的異常燃燒機(jī)理開展了一系列工作.Li等[10]以一臺(tái)PFI氫發(fā)動(dòng)機(jī)為研究對象進(jìn)行了壓縮比和進(jìn)氣溫度對爆震影響的試驗(yàn)研究,發(fā)現(xiàn)壓縮比和進(jìn)氣溫度是影響氫發(fā)動(dòng)機(jī)燃燒爆震極限當(dāng)量比的重要參數(shù).Szwaja等[11]發(fā)現(xiàn)氫發(fā)動(dòng)機(jī)在不同的壓縮比下發(fā)生的爆震有所不同,壓縮比在11以下時(shí)最大壓力振蕩幅值在0.1MPa以下,而壓縮比大于11時(shí)最大壓力振蕩幅值可能會(huì)突破一個(gè)數(shù)量級.Luo等[12]通過數(shù)值模擬方法,研究了氫發(fā)動(dòng)機(jī)的爆震誘發(fā)因素及爆震頻率,發(fā)現(xiàn)氫發(fā)動(dòng)機(jī)的異常燃燒現(xiàn)象存在相互促進(jìn)的關(guān)系,回火和早燃很大概率會(huì)誘發(fā)爆震;通過傅里葉變換分析得知,氫發(fā)動(dòng)機(jī)在各個(gè)模式下的爆震頻率都高于汽油機(jī),輕度爆震的壓力波沿徑向傳播,重度爆震的壓力波沿軸向傳播.Szwaja等[13]發(fā)現(xiàn),氫發(fā)動(dòng)機(jī)的爆震可以分為輕爆震和重爆震,輕爆震發(fā)生在燃燒初期,而重爆震發(fā)生在燃燒末期,重爆震會(huì)因?yàn)闊釕?yīng)力迅速損壞發(fā)動(dòng)機(jī).
盡管對PFI氫發(fā)動(dòng)機(jī)的燃燒及爆震已經(jīng)做了大量研究,但氫發(fā)動(dòng)機(jī)的燃燒技術(shù)仍然不成熟[14-15].研究發(fā)現(xiàn),氫發(fā)動(dòng)機(jī)存在不同強(qiáng)度的爆震,但是不同強(qiáng)度爆震的誘發(fā)原因尚不清楚(如燃燒速率過快和末端自燃均可能引起爆震),不同強(qiáng)度爆震之間的關(guān)聯(lián)也不明確,關(guān)于發(fā)動(dòng)機(jī)關(guān)鍵參數(shù)對燃燒及爆震強(qiáng)度的影響研究不夠完善.因此,本文以一臺(tái)PFI氫發(fā)動(dòng)機(jī)為研究對象,探究關(guān)鍵參數(shù)(點(diǎn)火時(shí)刻、當(dāng)量比)對PFI氫發(fā)動(dòng)機(jī)燃燒及爆震特性的影響,研究結(jié)果對于深入理解氫發(fā)動(dòng)機(jī)燃燒特性及不同強(qiáng)度爆震的誘發(fā)機(jī)理及從根本上尋求解決方法提供重要理論指導(dǎo).
本研究在一臺(tái)由General Motor 2.0T為原型機(jī)改造的進(jìn)氣道噴射式氫發(fā)動(dòng)機(jī)上進(jìn)行.該發(fā)動(dòng)機(jī)配備了可拆卸的活塞以便調(diào)節(jié)壓縮比,為了研究氫發(fā)動(dòng)機(jī)的燃燒及爆震特性,本文選擇了壓縮比為12的活塞.燃燒室由帶有4氣門(2個(gè)進(jìn)氣門、2個(gè)排氣門)的缸蓋及平頂活塞構(gòu)成,其內(nèi)徑是88mm,行程為105mm,保證了約0.64L的排量.此外,節(jié)氣門開度維持在8%左右,此時(shí)純壓縮的最大缸壓為2.47MPa,約為節(jié)氣門全開時(shí)的85%.圖1為發(fā)動(dòng)機(jī)臺(tái)架示意,詳細(xì)參數(shù)見表1.
圖1?發(fā)動(dòng)機(jī)臺(tái)架示意
表1?發(fā)動(dòng)機(jī)主要參數(shù)
Tab.1?Specifications of the test engine
試驗(yàn)發(fā)動(dòng)機(jī)由一臺(tái)直流測功機(jī)(DZDC-20S)控制,轉(zhuǎn)速維持在1000r/min,精度為±0.2%.上止點(diǎn)前280°CA時(shí),由電子控制單元(MOTEC M400)控制進(jìn)氣道噴射器以0.3MPa的壓力向缸內(nèi)噴射氫氣,噴射脈沖寬度與噴射量呈線性關(guān)系,當(dāng)量比由安裝在排氣管上的Bosch寬域氧傳感器測量,測量分辨率為0.1%,響應(yīng)時(shí)間為0.15s.本文通過調(diào)整噴射脈寬使當(dāng)量比分別等于0.5、0.6、0.7、0.8.
由于發(fā)動(dòng)機(jī)采用風(fēng)冷冷卻方式,無法長時(shí)間點(diǎn)火運(yùn)行,故選取了缸蓋溫度作為試驗(yàn)時(shí)的參考溫度,缸蓋溫度由一個(gè)安裝在缸蓋上的K型熱電偶測量,測量精度為±0.1℃,為盡量消除因缸體溫度高導(dǎo)致的測量結(jié)果失準(zhǔn),采用監(jiān)測缸蓋溫度后采集數(shù)據(jù)的方法,當(dāng)缸蓋溫度接近90℃時(shí),數(shù)據(jù)采集系統(tǒng)開始采集連續(xù)循環(huán)的熱力學(xué)數(shù)據(jù);當(dāng)缸蓋溫度超過95℃時(shí),發(fā)動(dòng)機(jī)停止運(yùn)行使其冷卻.缸內(nèi)壓力數(shù)據(jù)由一個(gè)Kistler 6125A型壓電式壓力傳感器和一臺(tái)Kistler 5018型電荷放大器測量,其采集分辨率可達(dá)0.1°CA.在發(fā)動(dòng)機(jī)運(yùn)行穩(wěn)定之后,數(shù)據(jù)采集系統(tǒng)連續(xù)采集50個(gè)循環(huán)下的熱力學(xué)數(shù)據(jù),所有的控制都基于電子控制單元.
壓力的采樣頻率為0.1°CA即60kHz,足夠捕捉爆震現(xiàn)象的壓力振蕩[16].應(yīng)用帶通濾波器從范圍為4~25kHz的原始缸內(nèi)壓力數(shù)據(jù)中分離爆震壓力[17].然后計(jì)算爆震強(qiáng)度(maximum amplitude of pressure oscillations,MAPO),其被定義為帶通濾波壓力跡線的絕對峰值[18].此外,基于熱力學(xué)第一定律的標(biāo)準(zhǔn)單區(qū)域模型計(jì)算熱釋放率(HRR)、燃燒持續(xù)期(combustion duration)和燃燒相位[19].
本文以平均指示壓力循環(huán)變動(dòng)系數(shù)(coefficients of variation of indicated mean effective pressure,COVIMEP)來表征發(fā)動(dòng)機(jī)的燃燒穩(wěn)定性,其計(jì)算式為
式中:IMEP是單個(gè)工況下每個(gè)循環(huán)的平均指示壓力;IMEPm是該工況下個(gè)循環(huán)的平均值;是該工況的循環(huán)數(shù).
對于進(jìn)氣道噴射式發(fā)動(dòng)機(jī)來說,點(diǎn)火時(shí)刻和當(dāng)量比對發(fā)動(dòng)機(jī)性能和燃燒過程有著顯著的影響,圖2和圖3分別給出了不同點(diǎn)火時(shí)刻和當(dāng)量比條件下的缸壓和放熱率.如圖2所示,在當(dāng)量比0.5的條件下,隨著點(diǎn)火時(shí)刻從-5°CA提前到-30°CA,燃燒相位逐漸提前,反應(yīng)速度加快,缸內(nèi)最大壓力峰值從5.18MPa先增大到6.1MPa又逐漸降低到5.9MPa,HRR從70.4J/(°CA)逐漸增大到97.8J/(°CA),放熱更加集中.如圖3所示,點(diǎn)火時(shí)刻固定在-25°CA條件下,隨著當(dāng)量比從0.5增大到0.7,燃燒相位提前、反應(yīng)速度加快、放熱更加集中,缸內(nèi)最大壓力峰值從5.8MPa增大到6.2MPa,HRR峰值從60.2J/(°CA)增大到97J/(°CA).
圖2?不同點(diǎn)火時(shí)刻下的缸內(nèi)壓力和放熱率
圖3?不同當(dāng)量比下的缸內(nèi)壓力和放熱率
圖4給出了不同點(diǎn)火時(shí)刻及當(dāng)量比條件下的IMEP及COVIMEP,用以表征發(fā)動(dòng)機(jī)的做功能力及燃燒穩(wěn)定性.從圖4(a)可以看出,在當(dāng)量比0.5條件下,隨著點(diǎn)火時(shí)刻從-30°CA推遲到-5°CA,平均指示壓力IMEP從0.11MPa逐漸增大到0.37MPa,發(fā)動(dòng)機(jī)做功能力逐漸增強(qiáng);將當(dāng)量比從0.5增大到0.7時(shí),發(fā)動(dòng)機(jī)IMEP整體呈減小趨勢.從圖4(b)可以看出,在當(dāng)量比0.5條件下,隨著點(diǎn)火時(shí)刻從-30°CA推遲到-5°CA,COVIMEP從37%逐漸降低到8%;將當(dāng)量比從0.5增大到0.7,由于混合氣濃度的增大使得缸內(nèi)燃燒更加劇烈,燃燒持續(xù)期明顯縮短,發(fā)動(dòng)機(jī)COVIMEP逐漸增大.
圖5給出了不同點(diǎn)火時(shí)刻和當(dāng)量比條件下的燃燒持續(xù)期,記錄為燃燒質(zhì)量分?jǐn)?shù)從CA10~CA90的曲軸轉(zhuǎn)角.當(dāng)量比為0.5時(shí),隨著點(diǎn)火時(shí)刻的推遲,燃燒持續(xù)期先增大后減小,燃燒持續(xù)期一般維持在10°CA左右,且增大當(dāng)量比會(huì)使燃燒持續(xù)期縮短.
當(dāng)量比增大會(huì)使得發(fā)動(dòng)機(jī)燃燒持續(xù)期對點(diǎn)火時(shí)刻的敏感性下降.由于氫發(fā)動(dòng)機(jī)燃燒持續(xù)期較短,當(dāng)點(diǎn)火時(shí)刻過于提前時(shí),整個(gè)燃燒過程發(fā)生在壓縮行程,即完全轉(zhuǎn)化為負(fù)功,所以IMEP較小,同時(shí)循環(huán)變動(dòng)較大.推遲點(diǎn)火時(shí)刻可以在低當(dāng)量比條件下提高發(fā)動(dòng)機(jī)做功能力的同時(shí)降低循環(huán)變動(dòng),但是在高當(dāng)量比條件下易誘發(fā)爆震燃燒.
圖5?不同點(diǎn)火時(shí)刻和當(dāng)量比下的燃燒持續(xù)期
為進(jìn)一步研究關(guān)鍵參數(shù)對氫發(fā)動(dòng)機(jī)爆震特性的影響,繼續(xù)增大當(dāng)量比進(jìn)行不同點(diǎn)火時(shí)刻對氫發(fā)動(dòng)機(jī)爆震特性的試驗(yàn)研究.通常將MAPO在一個(gè)或幾個(gè)MPa時(shí)的爆震定義為常規(guī)爆震,而將MAPO超過常規(guī)爆震一個(gè)甚至兩個(gè)數(shù)量級以上的爆震定義為超級爆震[20].為了研究不同情況下的PFI氫發(fā)動(dòng)機(jī)爆震的統(tǒng)計(jì)學(xué)特性,圖6分別給出了當(dāng)量比0.6、0.7、0.8下50個(gè)連續(xù)循環(huán)的詳細(xì)MAPO分布,分別對應(yīng)無爆震、輕爆震、超級爆震情況,并給出了平均爆震強(qiáng)度MAPO及MAPO相對標(biāo)準(zhǔn)偏差(relative standard deviation,RSD).
觀察平均MAPO發(fā)現(xiàn),在當(dāng)量比0.6沒有爆震發(fā)生的情況下,平均MAPO基本保持不變,維持在0.1MPa以下,RSD基本維持在0.15~0.35不變.
當(dāng)量比0.7時(shí),隨著點(diǎn)火時(shí)刻從-30°CA推遲到-5°CA,平均爆震強(qiáng)度MAPO呈現(xiàn)先增大后降低的趨勢,最大平均MAPO發(fā)生在-20°CA點(diǎn)火時(shí),約為0.22MPa;對于發(fā)生爆震的工況(點(diǎn)火時(shí)刻-20°CA、-15°CA、-10°CA),單個(gè)循環(huán)的MAPO分散在0.10~0.45MPa之間,最大MAPO發(fā)生在-20°CA點(diǎn)火時(shí),約為0.42MPa.綜上得知當(dāng)量比0.7時(shí)發(fā)生的爆震為一般強(qiáng)度爆震;無量綱數(shù)RSD基本保持不變,約為0.35~0.55,證明一般強(qiáng)度爆震主要取決于較大的燃燒放熱率或壓力升高率.
當(dāng)量比0.8時(shí),所有點(diǎn)火時(shí)刻均發(fā)生了爆震,平均MAPO隨點(diǎn)火時(shí)刻推遲呈現(xiàn)先增大后減小又增大的趨勢,最大平均MAPO發(fā)生在-15°CA,約為1MPa;單個(gè)循環(huán)MAPO分散在0.1~6.5MPa之間,最大MAPO發(fā)生在-15°CA點(diǎn)火時(shí),約為6.2MPa,此時(shí)的爆震強(qiáng)度較當(dāng)量比0.7時(shí)的爆震強(qiáng)度增大了一個(gè)數(shù)量級,為超級爆震;無量綱數(shù)RSD從-25°CA點(diǎn)火時(shí)的0.586增大到-15°CA點(diǎn)火時(shí)的1.405,隨機(jī)性增加,證明超級爆震的發(fā)生是由于隨機(jī)的熱點(diǎn)自燃引起的.
綜上研究發(fā)現(xiàn),每個(gè)當(dāng)量比下均存在一個(gè)最強(qiáng)爆震點(diǎn)火時(shí)刻(一般在-20°CA~-15°CA左右)使得氫發(fā)動(dòng)機(jī)爆震強(qiáng)度最大,以此為基準(zhǔn)提前或推遲點(diǎn)火時(shí)均使發(fā)動(dòng)機(jī)爆震強(qiáng)度減?。@與汽油機(jī)爆震表現(xiàn)出的規(guī)律是完全不同的[21],一般來說汽油機(jī)爆震強(qiáng)度隨著點(diǎn)火時(shí)刻推遲呈減小趨勢;同時(shí),兩種發(fā)動(dòng)機(jī)爆震強(qiáng)度對點(diǎn)火時(shí)刻的敏感度也不同,每推遲10°CA點(diǎn)火,氫氣發(fā)動(dòng)機(jī)爆震強(qiáng)度變化幅值很大,一般在0.2~0.8MPa左右,即氫氣發(fā)動(dòng)機(jī)爆震強(qiáng)度對點(diǎn)火時(shí)刻更敏感.
由以上得知當(dāng)量比0.8、點(diǎn)火時(shí)刻-15°CA時(shí)爆震概率最高且平均MAPO最大,因此對此工況展開著重分析.如圖7所示,前6個(gè)循環(huán)發(fā)生了一般強(qiáng)度爆震,MAPO從0.15MPa逐漸增加到0.75MPa,第7個(gè)循環(huán)發(fā)生了超級爆震,此刻MAPO較一般強(qiáng)度爆震增大一個(gè)數(shù)量級至3.8MPa,即誘發(fā)了超級爆震.在初始幾個(gè)循環(huán)中,隨著一般爆震強(qiáng)度的增加,缸內(nèi)部件被不斷加熱,一般爆震的累積作用使得缸內(nèi)部件出現(xiàn)局部過熱的現(xiàn)象,繼而誘發(fā)了超級爆震現(xiàn)象的發(fā)生.
圖6?不同當(dāng)量比下不同點(diǎn)火時(shí)刻時(shí)的詳細(xì)MAPO分布
如圖8所示,此工況下最強(qiáng)爆震循環(huán)為第14個(gè)循環(huán),此循環(huán)的缸內(nèi)最大壓力峰值達(dá)到12.8MPa、最大HRR達(dá)到280J/(°CA)、MAPO高達(dá)6.1MPa.將此循環(huán)的原始缸內(nèi)壓力曲線、經(jīng)過4~25kHz帶通濾波的壓力振蕩曲線以及放熱率曲線與一般爆震進(jìn)行比較.一般爆震循環(huán)的缸內(nèi)最大壓力峰值約為6.2MPa、最大HRR約為170J/(°CA)、最大MAPO約為0.25MPa.CAKO(the onset of pressure oscillation)定義為壓力振蕩開始時(shí)對應(yīng)的曲軸轉(zhuǎn)角,發(fā)現(xiàn)一般爆震情況的CAKO與瞬時(shí)放熱率峰值重合,說明一般爆震是由于高HRR引起,而超級爆震循環(huán)的瞬時(shí)放熱率呈現(xiàn)多段波動(dòng)上升趨勢.
圖7 初期7個(gè)循環(huán)的缸壓及壓力振蕩以及相應(yīng)的MAPO
圖8 不同強(qiáng)度爆震循環(huán)的原始缸內(nèi)壓力、放熱率及壓力振蕩
由圖9可知,提高當(dāng)量比使氫發(fā)動(dòng)機(jī)爆震強(qiáng)度增大.在當(dāng)量比從0.6增大到0.7時(shí),爆震強(qiáng)度在各個(gè)點(diǎn)火時(shí)刻下的增幅基本維持在0.2MPa以內(nèi).
圖9?不同點(diǎn)火時(shí)刻下不同當(dāng)量比的平均爆震強(qiáng)度
將當(dāng)量比從0.7增大到0.8發(fā)現(xiàn),平均爆震強(qiáng)度對當(dāng)量比的敏感性和點(diǎn)火時(shí)刻存在很大關(guān)聯(lián)性.具體表現(xiàn)在-20°CA及-15°CA左右點(diǎn)火時(shí),平均爆震強(qiáng)度對當(dāng)量比的敏感性較大,平均爆震強(qiáng)度隨著當(dāng)量比增大的增幅超過0.8MPa;提前或推遲點(diǎn)火時(shí),增大當(dāng)量比僅使得平均爆震強(qiáng)度小幅度增大,增幅均在0.1MPa左右.
將每個(gè)工況50個(gè)循環(huán)中MAPO大于0.1MPa的循環(huán)所占的比例定義為爆震概率.如圖10所示,增大當(dāng)量比使發(fā)動(dòng)機(jī)爆震概率增大.但爆震概率對當(dāng)量比的敏感性與點(diǎn)火時(shí)刻存在很大關(guān)聯(lián)性.具體體現(xiàn)在最強(qiáng)爆震點(diǎn)火時(shí)刻附近點(diǎn)火時(shí),不同當(dāng)量比下均存在較大爆震概率故增幅較小;以最強(qiáng)爆震點(diǎn)火時(shí)刻為基準(zhǔn)提前或推遲點(diǎn)火時(shí)刻,當(dāng)量比的增大使得爆震概率明顯增大,其中在-25°CA及-5°CA點(diǎn)火時(shí),增大當(dāng)量比使爆震概率增大70%.
圖10?不同點(diǎn)火時(shí)刻下不同當(dāng)量比的爆震概率
圖11所示為點(diǎn)火時(shí)刻-20°CA時(shí),不同當(dāng)量比條件下最強(qiáng)爆震循環(huán)原始缸內(nèi)壓力及壓力振蕩對比.由圖可知,增大當(dāng)量比使得缸內(nèi)反應(yīng)速度加快,缸內(nèi)最大壓力峰值從5.8MPa增大到9.3MPa,爆震強(qiáng)度從0.4MPa增加到4MPa,另外爆震起始時(shí)刻也從-8°CA提前到-12°CA.
圖11 相同點(diǎn)火時(shí)刻不同當(dāng)量比下的原始缸內(nèi)壓力及壓力振蕩
本文基于一臺(tái)進(jìn)氣道噴射式單缸氫發(fā)動(dòng)機(jī),開展了關(guān)鍵參數(shù)(點(diǎn)火時(shí)刻、當(dāng)量比)對發(fā)動(dòng)機(jī)燃燒及爆震特性影響的試驗(yàn)研究,主要結(jié)論如下.
(1) 點(diǎn)火時(shí)刻對氫發(fā)動(dòng)機(jī)燃燒過程有著顯著影響.持續(xù)提前點(diǎn)火時(shí)刻會(huì)使發(fā)動(dòng)機(jī)的做功能力降低,同時(shí)循環(huán)變動(dòng)增加.綜合發(fā)動(dòng)機(jī)做功能力和循環(huán)變動(dòng)來看,-15°CA左右點(diǎn)火時(shí)發(fā)動(dòng)機(jī)性能最優(yōu).
(2) 當(dāng)量比對氫發(fā)動(dòng)機(jī)做功能力和爆震燃燒具有重要作用.固定最佳點(diǎn)火時(shí)刻條件下,持續(xù)增大當(dāng)量比會(huì)使發(fā)動(dòng)機(jī)做功能力下降、循環(huán)變動(dòng)增大.不同當(dāng)量比下均存在最強(qiáng)的爆震點(diǎn)火時(shí)刻,一般是在-20°CA~-15°CA左右.
(3) 氫發(fā)動(dòng)機(jī)爆震強(qiáng)度對點(diǎn)火時(shí)刻和當(dāng)量比相當(dāng)敏感,且其對當(dāng)量比的敏感性與點(diǎn)火時(shí)刻存在很大關(guān)聯(lián).在爆震最強(qiáng)的點(diǎn)火時(shí)刻下增大當(dāng)量比可以使平均爆震強(qiáng)度顯著增大,最大增幅可達(dá)0.8MPa.同時(shí),高當(dāng)量比條件下,一般強(qiáng)度爆震不斷累加會(huì)誘發(fā)產(chǎn)生超級爆震.
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Experimental Investigations on Combustion and Knock Characteristics of Port Fuel Injection Hydrogen Engine
Wei Haiqiao1,Wang Nan1,Li Wei2,Jia Demin2,Li Jinguang1,Pan Jiaying1
(1. State Key Laboratory of Engines,Tianjin University,Tianjin 300072,China;2. Weichai Power Co.,Ltd.,Weifang 261041,China)
To explore the combustion and knock characteristics of a port fuel injection(PFI)hydrogen engine,this study investigates the effect of key parameters(ignition timing and equivalence ratio)on the combustion and knock characteristics of a four-stroke PFI hydrogen engine. In the experimental study,the ignition time varies from -5°CA to -30°CA and the equivalence ratio varies from 0.5 to 0.8. Results show that as the ignition time advances,the engine’s power gradually reduces,whereas the cycle’s variation gradually increases. When the equivalence ratio is increased from 0.5 to 0.7,the engine’s power reduces,whereas the cycle’s variation increases. From the perspective of comprehensive engine power and cycle variations,the engine performance is optimal when the ignition time is approximately -15°CA. The statistical analysis revealed that starting from an ignition time of -25°CA,with the ignition time delayed,the average knock intensity first increases and then decreases. Further,with increasing equivalence ratio,the average knock intensity increases;however,its sensitivity to the equivalence ratio is closely related to the ignition time. When the ignition time is between -15°CA and -20°CA,increasing the equivalence ratio will significantly increase the average knock intensity. Moreover,the sensitivity of the knock probability to the equivalence ratio is closely related to the ignition timing,i.e.,when the ignition time advances or delays,the sensitivity improves. Thus,increasing the equivalence ratio will significantly increase the knock probability and advance the knock onset time. In addition,at a high equivalence ratio,the cumulative effect of general intensity knock in the initial cycle will induce the occurrence of a super knock phenomenon.
hydrogen engine;combustion characteristics;knock;super knock;ignition time;equivalence ratio
10.11784/tdxbz202108042
TK448.21
A
0493-2137(2022)12-1230-07
2021-08-16;
2021-09-15.
衛(wèi)海橋(1974—??),男,博士,教授,whq@tju.edu.cn.
潘家營,jypan@tju.edu.cn.
國家自然科學(xué)基金資助項(xiàng)目(52076149,51825603).
Supported by the National Natural Science Foundation of China(No. 52076149,No. 51825603).
(責(zé)任編輯:金順愛)