JP4006733B2

JP4006733B2 - Method and apparatus for measuring mass concentration of soot aggregate in combustion exhaust

Info

Publication number: JP4006733B2
Application number: JP2002363517A
Authority: JP
Inventors: 武征神本
Original assignee: Tokai University Educational Systems
Current assignee: Tokai University Educational Systems
Priority date: 2002-12-16
Filing date: 2002-12-16
Publication date: 2007-11-14
Anticipated expiration: 2022-12-16
Also published as: JP2004198121A

Description

【０００１】
【発明の属する技術分野】
本発明は、燃焼系から排出されるすす（すす凝集体）の質量濃度を実時間で測定する燃焼排気中のすす凝集体の質量濃度測定方法及び装置に関するものである。
【０００２】
【従来の技術】
従来、排気中のすすに光を透過させてすす濃度を評価する測定装置としてオパシメータ（オーストリアＡＶＬ社製）があるが、光源に白色光を用いているため質量濃度を定量的に求めることができなかった。
【０００３】
なお、単色のレ−ザビームを排気中に透過させてすす粒子群の減衰係数を求めた研究（例えば非特許文献１参照）があるが、減衰係数における散乱係数の影響を無視しているため正確な質量濃度が求まるものでなかった。
【０００４】
また、ディーゼル排出すす濃度と粒子径を多波長のレーザビームを用いて減衰法により測定した研究（例えば非特許文献２）があるが、すす凝集体を球と仮定して計算しているため（例えば非特許文献３参照）に示されるように球の散乱係数は凝集体のそれと異なるため正確な質量濃度は求まらないものであっった。
【０００５】
また、燃焼排気中のすす質量濃度をすす凝集体理論を基礎として単色レーザ光減衰法により測定した研究（例えば非特許文献４参照）もある。しかし、散乱係数を計算するに際し、他の波長のレーザ光の情報ではなく電子顕微鏡で撮影したすすの情報を入力としている。
【０００６】
【非特許文献１】
Pablo Mitchell, Michael Frenklach "Monte Carlo Simulation of Soot Aggregation with Simultaneous Surface Growth-Why Primary Particles Appear Spherical" 27th Symp. om Comb. USA, Combustion Institute,1998, pp.1507-1514
【非特許文献２】
R.Zahoransky,W.Kuhnt,E.Laile "In‐line particle measurements of the undiluted exhaust of combustion engines by multi-wavelength extinction" J.Aerosol Sci., UK, Elsevier Science Ltd. 1997, vol.28,suppl.1. pp.549-550
【非特許文献３】
Richrd A.Dobbins and Constantine M.Megaridis "Absorption and scattering of light by poly-disperse aggregates" Applied optics, USA, Optical Society of America, 1991,vol.30,No.33, pp.4747-4754
【非特許文献４】
U. O. Koylu, G. M. Faeth "Structure of Overfire Soot in Buoyant Turbulent Diffusion Flames at Long Residence Times" Combustion and Flame, USA, Elsevier Science Publishing Co., Ink, 1992, No.89, pp.140-156
【０００７】
【発明が解決しようとする課題】
上述したように、従来、透過光減衰法によるすす質量濃度の測定が試みられた例はあるが、いずれも理論的かつ実験的な検討が不十分であり信頼性が極めて低く、散乱係数を考慮したものであっても、電子顕微鏡で撮影したすすの情報を入力としているため簡便な方法とは言いがたいものであった。
【０００８】
よって、本発明は、排気流中のすす凝集体の質量濃度を理論的根拠に基づいてすす凝集体による散乱を考慮して簡便に測定することができる燃焼排気中のすす凝集体の質量濃度測定方法及び装置を提供することを課題としている。
【０００９】
本発明はまた、排気流中のすす凝集体の質量濃度を理論的根拠に基づいて散乱係数を考慮して実時間で且つ簡便に測定することができる燃焼排気中のすす凝集体の質量濃度測定方法及び装置を提供することを課題としている。
【００１０】
【課題を解決するための手段】
上記の課題を解決するためなされた請求項１記載の発明は、すす凝集体群を含む燃焼排気流に透過させた異なる波長を有する二本の光線の透過率の対数比に対する散乱影響因子の値の関係を予め求めておき、すす凝集体群を含む測定対象の燃焼排気流に前記二本の光線を透過させて測定した各波長の透過率に対応する散乱影響因子の値を前記予め求めておいた関係によって決定し、該決定した散乱影響因子の値を用い、すす凝集体に入射した光線が吸収と散乱によって減衰する程度を表す係数である比減衰係数を算出し、該算出した比減衰係数と前記一方の光線の減衰率とを予め定めた演算式に代入し演算して質量濃度を測定することを特徴とする燃焼排気中のすす凝集体の質量濃度測定方法に存する。
【００１１】
請求項１記載の発明によれば、すす凝集体群を含む燃焼排気流に異なる波長を有する二本の光線を透過させることによって、波長が異なることによって二波長に顕著化する散乱の影響を、二波長の透過率の対数比に対する散乱影響因子の値の関係として予め求めておき、すす凝集体群を含む測定対象の燃焼排気流に二本の光線を透過させて測定した各波長の透過率に対応する散乱影響因子の値を予め求めておいた関係によって決定し、この決定した散乱影響因子の値を用い、すす凝集体に入射した光線が吸収と散乱によって減衰する程度を表す係数である比減衰係数を算出し、この算出した比減衰係数と一方の光線の減衰率とを予め定めた演算式に代入し演算して質量濃度を測定するようにしているので、二波長の透過率の対数比に対する散乱影響因子の値の関係を予め求めておくだけで、排気流中のすす凝集体の質量濃度をすす凝集体による散乱を考慮して簡便に測定することができる。
【００１２】
請求項２記載の本発明は、すす凝集体群を含む燃焼排気流に透過させた異なる波長を有する二本の光線の透過率の対数比と、当該対数比に対応する散乱影響因子の値との関係を予め求めておき、すす凝集体群を含む測定対象の燃焼排気流に前記二本の光線を透過させて各波長の透過率を予め定めた所定間隔でそれぞれ測定し、該測定毎に、測定した二波長の透過率の対数比に対応する散乱影響因子の値を前記予め求めておいた関係によって決定し、該決定した散乱影響因子の値を用い、すす凝集体に入射した光線が吸収と散乱によって減衰する程度を表す係数である比減衰係数を算出し、該算出した比減衰係数と前記一方の光線の減衰率とを予め定めた演算式に代入し演算して質量濃度を測定することを特徴とする燃焼排気中のすす凝集体の質量濃度測定方法に存する。
【００１３】
請求項２記載の発明によれば、すす凝集体群を含む燃焼排気流に異なる波長を有する二本の光線を透過させることによって、波長が異なることによって二波長に顕著化する散乱の影響を、二波長の透過率の対数比に対する散乱影響因子の値の関係として予め求めておき、すす凝集体群を含む測定対象の燃焼排気流に二本の光線を透過させて各波長の透過率を予め定めた所定間隔でそれぞれ測定し、測定毎に、測定した二波長の透過率の対数比に対応する散乱影響因子の値を予め求めておいた関係によって決定し、この決定した散乱影響因子の値を用い、すす凝集体に入射した光線が吸収と散乱によって減衰する程度を表す係数である比減衰係数を算出し、この算出した比減衰係数と一方の光線の減衰率とを予め定めた演算式に代入し演算して質量濃度を測定するようにしているので、二波長の透過率の対数比に対する散乱影響因子の値の関係を予め求めておき、二波長の透過率の測定を所定間隔で行うだけで、排気流中のすす凝集体の質量濃度をすす凝集体による散乱を考慮して実時間で簡便に測定することができる。
【００１４】
請求項３記載の本発明は、すす凝集体群を含む燃焼排気流に透過させた異なる波長を有する二本の光線の透過率の対数比に対応する散乱影響因子の値の関係を予め求めておき、すす凝集体群を含む測定対象の燃焼排気流に前記二本の光線を透過させて測定した各波長の透過率に対応する散乱影響因子の値を前記予め求めておいた関係によって決定し、該決定した散乱影響因子の値を用いて前記二本の光線のうちの一方の光線における比散乱係数の比吸収係数に対する比を算出し、該算出した比と前記一方の光線について予め算出されている比吸収係数とによって、すす凝集体に入射した光線が減衰する程度を表す係数である比減衰係数を算出し、該算出した比減衰係数と前記一方の光線の減衰率とを予め定めた演算式に代入し演算して質量濃度を測定することを特徴とする燃焼排気中のすす凝集体の質量濃度測定方法に存する。
【００１５】
請求項３記載の発明によれば、すす凝集体群を含む燃焼排気流に異なる波長を有する二本の光線を透過させることによって、波長が異なることによって二波長に顕著化する散乱の影響を、二波長の透過率の対数比に対する散乱影響因子の値の関係として予め求めておき、すす凝集体群を含む測定対象の燃焼排気流に二本の光線を透過させて測定した各波長の透過率に対応する散乱影響因子の値を予め求めておいた関係によって決定し、この決定した散乱影響因子の値を用いて二本の光線のうちの一方の光線における比散乱係数の比吸収係数に対する比を算出し、この算出した比と一方の光線について予め算出されている比吸収係数とによって、すす凝集体に入射した光線が減衰する程度を表す係数である比減衰係数を算出し、この算出した比減衰係数と一方の光線の減衰率とを予め定めた演算式に代入し演算して質量濃度を測定するようにしているので、二波長の透過率の対数比に対する散乱影響因子の値の関係を予め求めておき、かつ吸収要因は一定であるとして比吸収係数を予め算出しておくだけで、排気流中のすす凝集体の質量濃度をすす凝集体による散乱を考慮して簡便に測定することができる。
【００１６】
請求項４記載の本発明は、請求項１又は２記載のにおいて、前記演算式は、前記比減衰係数をσext 、前記一方の光線の減衰率をτ、前記質量濃度をＣm 、前記光線が透過する光路長をＬとしたとき、
Ｃm ＝−ｌｎτ／σext Ｌ
で表される
ことを特徴とする請求項１〜３の何れかに記載の燃焼排気中のすす凝集体の質量濃度測定方法に存する。
【００１７】
請求項４記載の発明によれば、質量濃度の一般的な演算式を用いて測定を行うことができる。
【００１８】
請求項５記載の本発明は、すす凝集体群を含む測定対象の燃焼排気流に異なる波長を有する二本の光線を透過させて各波長の透過率をそれぞれ測定する透過率測定手段と、すす凝集体群を含む燃焼排気流に透過させた前記二本の光線の透過率の対数比に対応する散乱影響因子の値の関係を予め格納した格納手段と、前記測定手段による測定毎に、測定した二波長の透過率の対数比に対応する散乱影響因子の値を前記格納手段に格納されている前記関係によって決定し、該決定した散乱影響因子の値を用い、すす凝集体に入射した光線が吸収と散乱によって減衰する程度を表す係数である比減衰係数を算出し、該算出した比減衰係数と前記一方の光線の減衰率とを予め定めた演算式に代入し質量濃度を演算する演算手段とを備えることを特徴とする燃焼排気中のすす凝集体の質量濃度測定装置に存する。
【００１９】
請求項４記載の発明によれば、透過率測定手段が、すす凝集体群を含む測定対象の燃焼排気流に異なる波長を有する二本の光線を透過させて各波長の透過率をそれぞれ測定し、格納手段が、すす凝集体群を含む燃焼排気流に透過させた前記二本の光線の透過率の対数比に対応する散乱影響因子の値の関係を予め格納していて、演算手段が、測定手段による測定毎に、測定した二波長の透過率の対数比に対応する散乱影響因子の値を格納手段に格納されている関係によって決定し、この決定した散乱影響因子の値を用い、すす凝集体に入射した光線が吸収と散乱によって減衰する程度を表す係数である比減衰係数を算出し、この算出した比減衰係数と一方の光線の減衰率とを予め定めた演算式に代入し質量濃度を演算するので、請求項１記載の発明と同様に、二波長の透過率の対数比に対する散乱影響因子の値の関係を予め求めておくだけで、排気流中のすす凝集体の質量濃度をすす凝集体による散乱を考慮して簡便に測定することができる。
【００２０】
請求項６記載の本発明は、前記透過率測定手段は、異なる波長を有する二本の光線を同軸化してすす凝集体群を含む燃焼排気流に導く手段と、燃焼排気流の一部をサンプルして流す測定流路と、該測定流路の軸方向に沿って光線を入射するための光学窓と、排気中のすす粒子群を透過した光線を出射するための光学窓とが設けられた測定光学系と、出射した同軸の二本の光線を再び分離するための２枚の狭帯域フィルターと各フィルターを透過した透過光の強度を検出するフォトセンサーから成る光検出装置と、前記二波長の検出光強度信号をディジタル変換し、該変換によって得たディジタルデータを蓄積する信号処理手段と、前記ディジタルデータに基づいて各波長の透過率を演算する演算手段とを有することを特徴とする請求項５記載の燃焼排気中のすす凝集体の質量濃度測定装置に存する。
【００２１】
請求項６記載の発明によれば、透過率測定手段において、測定光学系には、異なる波長を有する二本の光線を同軸化してすす凝集体群を含む燃焼排気流に導く手段と、燃焼排気流の一部をサンプルして流す測定流路と、該測定流路の軸方向に沿って光線を入射するための光学窓と、排気中のすす粒子群を透過した光線を出射するための光学窓とが設けられ、かつ、光検出装置が、出射した同軸の二本の光線を再び分離するための２枚の狭帯域フィルターと各フィルターを透過した透過光の強度を検出するフォトセンサーから成り、二波長の検出光強度信号を信号処理手段がディジタル変換して蓄積したディジタルデータに基づいて演算手段が各波長の透過率を演算するので、燃焼排気流に影響を与えずに、燃焼排気流に相当のものに異なる波長を有する二本の光線を同軸化して導いて透過させ、かつ、質量濃度演算のための二波長の透過率を演算するたの透過光の強度を検出することができる。
【００２４】
【発明の実施の形態】
以下、本発明による燃焼排気中のすす凝集体の質量濃度測定方法を、該方法を実施する装置を示す図１を参照して詳細に説明するが、その前に、本発明の原理について説明する。
【００２５】
平行光線が透過する雰囲気中に存在する、光透過を減衰させるすすの質量濃度について、次式（１）で表されるBouguer Lambertの法則が成立することが知られている。
Ｃm ＝−ｌｎτ／σext Ｌ（１）
式（１）中、τは透過率、Ｌは光路長、σext は比減衰係数である。透過率τは測定値であり、光路長Ｌは装置固有の値であるので、共に容易に与えられる。比減衰係数σext はすす凝集体（直径３０ｎｍ程度の要素すすが数百個凝集したすす）に入射した平行光線が減衰する程度を表す係数であり、次式のように比吸収係数σabs と比散乱係数σsca の和として表される。
σext ＝σabs ＋σsca （２）
【００２６】
そこで、本発明では、比吸収係数σabs と比散乱係数σsca を理論的かつ実験的に決定し、透過率の測定からすすの質量濃度Ｃm を理論的根拠に基づいて測定精度と信頼性を格段に向上して実時間で且つ簡便に測定することができるようにするものである。
【００２７】
次に、すす凝集体に対する透過光減衰の理論を説明する。すす凝集体群に波長λの平行光線を入射した場合、透過率τは次式で与えられる。ただし、Ｉo は入射光強度、Ｉは透過光強度、Ｌは光路長である。
τ＝Ｉ／Ｉo ＝ｅｘｐ（−σextＣm Ｌ）（３）
σextは比減衰係数（ｍ²／ｋｇ）、Ｃm はすす凝集体の質量濃度（ｋｇ／ｍ^{3 )}であり、上式（２）は式（３）をＣm について整理して対数表記したものである。また、式（２）は次式（４）のように表される。
【数１】

【００２８】
上式（４）中、Ｅ（ｍ）、Ｆ（ｍ）は複素屈折率ｍの関数、λは波長、αp ＝πｄ／λ、ｄはすす凝集体を構成する要素すす粒子の直径、ｎpaはすす凝集体を構成する要素すす粒子数の平均値、ｆn はすす凝集体の大きさの分布幅を示す因子、ｋf はすす凝集体の形状を表す因子、Ｄf はすす凝集体の形状を表すフラクタ次元である。
上式（４）は次式のように書き替えることができる。
σext ＝σabs （１＋ρsa）（５）
式（５）中、ρsaは比散乱係数の比吸収係数に対する比であり、次式（６）のようになる。
【数２】

【００２９】
上式（６）から、ρsaはｎp が小さい場合は０であり、十分大きい場合は次式（７）のような一定値に漸近する。
【数３】

【００３０】
上式（６）中のＤf は略１．７５であることが知られており、またα＝πｄ／λ中のｄは電子顕微鏡写真より３０．３５ｎｍであることが分かっている。残る３つの未知のパラメータをひとまとめにしてＣ（散乱影響因子と呼ぶ）とおくと、次式（８）のようになる。
【数４】

【００３１】
これらの値を上式（６）に代入し、さらに式（６）を式（５）及び式（３）に代入して二波長における透過率τ1 及びτ2 の対数比と散乱影響因子Ｃとの関係を計算すると、図２のようなグラフが得られる。
【００３２】
例えば、測定値がｌｎτ2 ／ｌｎτ1 ＝０．７８であれば図２よりＣ＝５．５と決定される。Ｃ＝５．５の場合、λ1 ＝６３５ｎｍとλ2 ＝７６０ｎｍについてｎp とρsaの関係を計算すると図３のようになる。図中、縦軸の１．０が吸収分を表し、１以上の部分が散乱分を表す。Ｋf が６と９の場合について計算しており、添え字１が６３５ｎｍ、添え字２が７６０ｎｍに対応している。
【００３３】
一般に要素すす粒子数ｎp の数は約２００であり、図３より例えば６３５ｎｍの場合、比散乱係数の比吸収係数に対する比ρsaは０．１９〜０．２０であることが分かる。すなわち、減衰における散乱と吸収の比率ρsaを凝集体理論と透過率の測定値から決定することができる。
【００３４】
なお、比吸収係数σabs は定常運転におけるフィルタ法により測定したすす質量濃度と透過光減衰法による測定値が一致するように以下の手順で決定する。
【００３５】
まず、代表的な条件の定常運転時にペーパーフィルタ法で測定したすす質量濃度とある波長における透過率の測定値から計算したすす質量濃度が一致するように比減衰係数σext を決定する。
【００３６】
次に、同時に上記の定常運転時に２つの波長λ1 とλ2 における透過率τ1 とτ2 を測定し、これから得られるｌｎτ2 ／ｌｎτ1 の値を先に求めておいた図２に代入して散乱影響因子Ｃを決定する。
【００３７】
この散乱影響因子Ｃを用いて作図した図３に例えば通常のディーゼル機関から排出されるすす凝集体を構成する要素すす数ｎp ＝２００を当てはめると、比散乱係数と比吸収係数の比ρsaが決定できる。
【００３８】
上式（２）に示したσext ＝σabs (１＋ρsa）の関係があるから、ここで決定した比ρsaと先に決定した比減衰係数σext を代入すれば比吸収係数σabs が決まる。
【００３９】
比吸収係数σabs は理論的に上式（４）の右辺の第１項で与えられているので、波長λと決定した比吸収係数σabs をこの式に代入すれば複素屈折率ｍ＝ｎ−ｉｋの関数Ｅ（ｍ）が決まる。複素屈折率ｍの値は従来の研究によると、研究者によって少しずつ異なる値が提唱されているが、Ｅ（ｍ）の値が決まればこの値に対応するｍを決定することができる。
【００４０】
なお、関数Ｅ（ｍ）及びＦ（ｍ）は次式（９）及び（１０）によって表されるものである。
【数５】

【００４１】
以上のように、定常運転時の比吸収係数σabs 、比散乱係数σsca と比吸収係数σabs の比ρsaが決まり、比減衰係数σext が決定されるので、当該波長における透過率を測定すればすすの質量濃度Ｃm を測定することができる。
【００４２】
上述したようにして求めた定常運転時の比吸収係数σabs の値は、過渡運転時にも使ってよい。しかし、すす凝集体の寸法の分布とすす凝集体の形状、すす凝集体の平均的な大きさなどの関数である散乱影響因子Ｃによって影響を受ける。したがって、過渡運転時には実時間ベースでｌｎτ2 ／ｌｎτ1 を測定し、その値に応じて散乱影響因子Ｃを決定する必要がある。このＣから各時刻の比散乱係数σsca と比吸収係数σabs の比ρsaを算出することにより正しく過渡的運転時の比減衰係数σext を得ることができる。
【００４３】
図１に戻って、本発明の方法を実施する装置について説明する。図１において、燃焼装置の排気管１の途中あるいは出口に、排気をサンプルする流路２を設け、サンプルした排気を外部の測定流路３に導く。この測定流路３の両端には光線を入射、出射するための光学窓４，５がそれぞれ一個づつ設けている。また、この光学窓と測定流路内壁にすすが付着するのを防止するため加熱装置６，７とキャリブレーション用の空気パージ装置８が付設されている。なお、１ａは、測定流路３にサンプル排気が入り易くするため排気管１内に設けられた絞りである。
【００４４】
異なる波長を有する２本のダイオードレーザ９，１０からでた２本の光線はプリズム１１によって同軸化される。この光線はビームエキスパンダ１２を通って光学窓４から測定流路３に入り、すす粒子群によって減衰したのち光学窓５を通って検出系へ導かれる。
【００４５】
検出系では同軸化された２本の光線をビームスプリッタ１３で２方向の光線に分けたのち、それぞれの光線を狭帯域レーザフィルタ１４，１５に通すことにより光源のレーザ波長を持つ２本の光線に分離する。２本の光線の光の強度はフォトダイオード１６，１７によって検出される。検出されたアナログ信号は信号処理手段としての信号処理装置１８において実時間ベースでＡ／Ｄ変換されたのちディジタルデータとして記憶蓄積される。２つの波長の透過率に対応する２組のディジタルデータ列は演算用のパーソナルコンピュータ（パソコン）１９に転送される。
【００４６】
パソコン１９では、各波長の透過率の対数比を計算し、予めすす凝集体の光理論にもとづいて計算した関係式にこの対数比を代入することにより当該データ採取時のσsca ／σabs 、すなわち、比散乱係数の比吸収係数に対する比ρsaの値を決定し得る。図２に波長に６３５ｎｍと７８０ｎｍを用いた場合の透過率の対数比とσsca ／σabs を決定するための散乱影響因子Ｃの関係を示す。さらにＣの値と別途定常運転時に検定して求めておいた比吸収係数σabs の値を用いて比減衰係数σext を決定すれば、二波長のうちいずれかの波長λにおける透過率の測定値を上式（１）に代入することによってすす粒子の質量濃度Ｃｍが計算できる。
【００４７】
以上説明した実施形態では、燃焼排気流の一部をサンプルし、この流れの中のすす粒子群に波長の異なる２本の光線を同軸で入射してそれぞれの透過率を計測した後、両透過率の対数比からσsca/σabsを理論的に求め、さらに別途検定により求めたσabsを用いて透過率の測定値からすすの質量濃度を演算する構成を有するものと見ることができる。
【００４８】
また、実施形態では、排気流をサンプルする流路２、二波長の光線を同軸化してすす粒子群を含む排気流に入射する光学系、光線が透過する測定流路３、透過した同軸２本の光線を波長によって再分離してそれぞれの強度を検出する光学・検出系、得られたアナログ信号をディジタル化する信号処理装置１８を備え、パソコン１９がディジタル信号からすす質量濃度を演算する演算部として機能していると見ることができる。
【００４９】
さらに、実施の形態では、すす凝集体群を含む測定対象の燃焼排気流に異なる波長を有する二本の光線を透過させて各波長の透過率をそれぞれ測定する透過率測定手段は、異なる波長を有する二本の光線を同軸化してすす凝集体群を含む燃焼排気流に導く手段としての２本のダイオードレーザ９，１０、プリズム１１と、測定流路３と、光学窓４と、光学窓５とが設けられた測定光学系と、２枚の狭帯域フィルター１４，１５とフォトセンサー１６，１７から成る光検出装置と、信号処理装置１８と、ディジタルデータに基づいて各波長の透過率を予め定めたプログラムに従って演算する演算手段を構成するパソコン１９とによって実現されていると見ることができる。
【００５０】
また、すす凝集体群を含む燃焼排気流に透過させた前記二本の光線の透過率の対数比に対応する散乱影響因子の値の関係を予め格納する格納手段は、パソコン１９内の図示しないメモリによって構成され、メモリ内に、図２に示す関係がデータの形で格納されたり、或いは、図２に示す関係が近似式の形で格納される。
【００５１】
また、透過率の測定毎に、測定した二波長の透過率の対数比に対応する散乱影響因子の値を前記格納手段に格納されている関係によって決定し、該決定した散乱影響因子の値を用い、すす凝集体に入射した光線が吸収と散乱によって減衰する程度を表す係数である比減衰係数を算出し、該算出した比減衰係数と一方の光線の減衰率とを予め定めた演算式に代入し質量濃度を演算する演算手段は、パソコン１９を予め定めたプログラムに従って動作させることによって実現される。なお、質量濃度を演算するため、比減衰係数と光線の減衰率とが代入される演算式は、パソコン１９のメモリ内にプログラムの一部として格納される。
【００５２】
以上説明した実施形態の装置によれば、比吸収係数σabs と比散乱係数σsca を理論的かつ実験的に決定し、透過率τの測定からすすの質量濃度Ｃm を測定する方法の精度と信頼性を格段に向上することができる。
【００５３】
また、すす粒子の排出質量濃度（標準大気換算下における単位体積中の質量）の測定については、従来の方法は前述のごとく排気中のすす濃度を相対的あるいは定性的に評価しているに過ぎないのに対し、本発明では排気流中のすす粒子の質量濃度を理論的根拠にもとづいた簡便な装置を用いて実時間で測定しようとすることができるものである。
【００５４】
また、異なる波長を有する２本のダイオードレーザビームをディーゼル排気に透過させ、透過光減衰法によりすす凝集体の質量濃度を実時間で定量測定するので、二波長の対数透過率比から凝集体の散乱光影響要因を決定することにより測定精度と信頼性を向上することができる。
【００５５】
また、応答性は排気ガスがサンプルラインと測定流路を通過する時間で決まるので高応答性（０．２秒程度）を有する。
【００５６】
さらに、光強度の絶対値でなく相対値である透過率を測定するので検定が不要であり、且つ高安定性を有する。
【００５７】
さらにまた、光路長さを伸ばすことにより１ｍｇ／ｍ³レベルの低質量濃度の測定が可能である。
【００５８】
【発明の効果】
以上説明したように、請求項記載の本発明は、排気流中のすす凝集体の質量濃度を理論的根拠に基づいてすす凝集体による散乱を考慮して簡便に、又は、実時間で且つ簡便に測定することができる燃焼排気中のすす凝集体の質量濃度測定方法及び装置を提供することができる。
【図面の簡単な説明】
【図１】本発明による方法を実施するすす凝集体の質量濃度測定装置の一実施の形態を示す全体図である．
【図２】二波長の透過率の対数比からσsca/σabsを決めるための散乱影響因子Ｃを求めるための線図例である．
【図３】すす凝集体を構成する要素すす粒子数ｎp と、比散乱係数の比吸収係数に対する比ρsaとの関係を示す線図例である。
【符号の説明】
１排気管
２分流する流路
３測定流路
４，５光学窓
６，７加熱装置
８空気パージ装置
９，１０ダイオードレーザ
１１プリズム
１２ビームエキスパンダ
１３ビームスプリッタ
１４，１５狭帯域レーザフィルタ
１６，１７フォトダイオード
１８信号処理手段（信号処理装置）
１９パーソナルコンピュータ（演算手段）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for measuring the mass concentration of soot aggregates in combustion exhaust gas, which measures the mass concentration of soot (soot aggregates) discharged from a combustion system in real time.
[0002]
[Prior art]
Conventionally, there is an opacimeter (manufactured by Austria AVL) as a measuring device for evaluating the concentration of soot by transmitting light through soot in exhaust gas. However, since white light is used as a light source, the mass concentration can be obtained quantitatively. There wasn't.
[0003]
In addition, there is a study (for example, see Non-Patent Document 1) in which the attenuation coefficient of the soot group is obtained by transmitting a monochromatic laser beam into the exhaust gas. However, since the influence of the scattering coefficient on the attenuation coefficient is ignored, it is accurate. A high mass concentration could not be obtained.
[0004]
In addition, there is a study (for example, Non-Patent Document 2) in which the concentration and particle size of diesel exhaust are measured by an attenuation method using a multi-wavelength laser beam, but because soot agglomerates are calculated as spheres ( For example, as shown in Non-Patent Document 3), since the scattering coefficient of a sphere is different from that of an aggregate, an accurate mass concentration cannot be obtained.
[0005]
In addition, there is a study (for example, see Non-Patent Document 4) in which soot mass concentration in combustion exhaust gas is measured by a monochromatic laser light attenuation method based on a soot aggregate theory. However, when calculating the scattering coefficient, soot information taken with an electron microscope is used as input instead of information on laser light of other wavelengths.
[0006]
[Non-Patent Document 1]
Pablo Mitchell, Michael Frenklach "Monte Carlo Simulation of Soot Aggregation with Simultaneous Surface Growth-Why Primary Particles Appear Spherical" 27th Symp.om Comb.USA, Combustion Institute, 1998, pp.1507-1514
[Non-Patent Document 2]
R. Zahoransky, W. Kuhnt, E. Laile "In-line particle measurements of the undiluted exhaust of combustion engines by multi-wavelength extinction" J. Aerosol Sci., UK, Elsevier Science Ltd. 1997, vol. 28, suppl. 1.pp.549-550
[Non-Patent Document 3]
Richrd A. Dobbins and Constantine M. Megaridis "Absorption and scattering of light by poly-disperse aggregates" Applied optics, USA, Optical Society of America, 1991, vol. 30, No. 33, pp. 4747-4754
[Non-Patent Document 4]
U. O. Koylu, G. M. Faeth "Structure of Overfire Soot in Buoyant Turbulent Diffusion Flames at Long Residence Times" Combustion and Flame, USA, Elsevier Science Publishing Co., Ink, 1992, No. 89, pp.140-156
[0007]
[Problems to be solved by the invention]
As mentioned above, there have been examples of attempts to measure soot mass concentration by the transmitted light attenuation method. However, theoretical and experimental studies have been insufficient, and reliability has been extremely low. However, it is difficult to say that it is a simple method because it uses soot information taken with an electron microscope as input.
[0008]
Therefore, the present invention is able to easily measure the mass concentration of soot aggregates in the exhaust flow in consideration of scattering by the soot aggregates based on the theoretical basis. It is an object to provide a method and an apparatus.
[0009]
The present invention is also capable of measuring the mass concentration of soot aggregates in combustion exhaust gas, which can be measured in real time and simply in consideration of the scattering coefficient based on a theoretical basis. It is an object to provide a method and an apparatus.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the invention according to claim 1 is characterized in that the value of the scattering influencing factor with respect to the logarithmic ratio of the transmittance of two light beams having different wavelengths transmitted through the combustion exhaust stream containing the soot aggregate group. The scattering influence factor value corresponding to the transmittance of each wavelength measured by transmitting the two light beams through the combustion exhaust stream to be measured including the soot aggregate group is obtained in advance. The specific attenuation coefficient, which is a coefficient representing the degree to which the light incident on the soot aggregate is attenuated by absorption and scattering, is calculated using the determined scattering influence factor value, and the calculated specific attenuation The present invention resides in a method for measuring the mass concentration of soot agglomerates in combustion exhaust gas, wherein the mass concentration is measured by substituting the coefficient and the attenuation rate of the one light beam into a predetermined arithmetic expression.
[0011]
According to the invention described in claim 1, by transmitting two light beams having different wavelengths to the combustion exhaust stream containing the soot aggregate group, the influence of scattering that becomes noticeable in two wavelengths due to different wavelengths is obtained. The transmittance of each wavelength measured in advance by measuring the relationship between the logarithmic ratio of the transmittance of two wavelengths and the value of the scattering influencing factor and transmitting two light beams through the combustion exhaust stream to be measured including the soot aggregate group. Is a coefficient that represents the degree to which light rays incident on soot aggregates are attenuated by absorption and scattering using the determined scattering influence factor value. Since the specific attenuation coefficient is calculated, and the calculated specific attenuation coefficient and the attenuation factor of one of the rays are substituted into a predetermined calculation formula to calculate the mass concentration, the transmittance of the two wavelengths is measured. Logarithm to log ratio In the relationship between the values of the influencing factors just previously obtained, the mass concentration of soot aggregates in the exhaust stream can be easily measured in consideration of scattering by soot aggregates.
[0012]
The present invention according to claim 2 is a logarithmic ratio of the transmittance of two light beams having different wavelengths that are transmitted through a combustion exhaust stream containing soot aggregates, and a value of a scattering influencing factor corresponding to the logarithmic ratio. , And the transmittance of each wavelength is measured at predetermined intervals by transmitting the two light beams through the combustion exhaust stream to be measured including the soot aggregate group. The scattering influence factor value corresponding to the logarithmic ratio of the measured two-wavelength transmittance is determined according to the previously determined relationship, and the light incident on the soot aggregate is determined using the determined scattering influence factor value. Calculate the specific attenuation coefficient, which is a coefficient representing the degree of attenuation by absorption and scattering, and calculate the mass concentration by substituting the calculated specific attenuation coefficient and the attenuation rate of the one light ray into a predetermined calculation formula. Of soot aggregates in combustion exhaust It resides in the amount concentration measuring method.
[0013]
According to the invention described in claim 2, by transmitting two light beams having different wavelengths to the combustion exhaust stream containing the soot aggregate group, the influence of scattering that becomes noticeable in two wavelengths due to different wavelengths is obtained. The relationship between the logarithmic ratio of the transmittance of the two wavelengths and the value of the scattering influence factor is obtained in advance, and two light beams are transmitted through the combustion exhaust stream to be measured including the soot aggregate group so that the transmittance of each wavelength is determined in advance. Each measurement is performed at a predetermined interval, and for each measurement, the value of the scattering influence factor corresponding to the logarithmic ratio of the measured transmittance of the two wavelengths is determined in advance, and the value of the determined scattering influence factor is determined. Is used to calculate a specific attenuation coefficient, which is a coefficient representing the degree to which light rays incident on the soot aggregate are attenuated by absorption and scattering, and the calculated specific attenuation coefficient and the attenuation rate of one of the light beams are calculated in advance. Assign to and calculate Since the quantity concentration is measured, the relationship between the value of the scattering influence factor to the logarithmic ratio of the two-wavelength transmittance is obtained in advance, and the two-wavelength transmittance is measured at predetermined intervals. The mass concentration of the soot aggregate can be easily measured in real time in consideration of scattering by the soot aggregate.
[0014]
According to the third aspect of the present invention, the relationship between the values of the scattering influencing factors corresponding to the logarithmic ratio of the transmittances of two light beams having different wavelengths transmitted through the combustion exhaust stream containing the soot aggregate group is obtained in advance. In addition, the value of the scattering influence factor corresponding to the transmittance of each wavelength measured by transmitting the two light beams through the combustion exhaust stream to be measured including the soot aggregate group is determined according to the relationship obtained in advance. The ratio of the specific scattering coefficient of one of the two light beams to the specific absorption coefficient is calculated using the determined value of the scattering influence factor, and the calculated ratio and the one light beam are calculated in advance. A specific attenuation coefficient, which is a coefficient representing the degree to which light rays incident on the soot aggregate are attenuated, and the calculated specific attenuation coefficient and the attenuation factor of the one light beam are determined in advance. Substituting into the equation and calculating the mass It consists in mass concentration measurement method of soot aggregates in the combustion exhaust gas and measuring the.
[0015]
According to the invention of claim 3, by transmitting two light beams having different wavelengths to the combustion exhaust stream containing the soot aggregate group, the influence of scattering that becomes noticeable in two wavelengths due to different wavelengths is obtained. The transmittance of each wavelength measured in advance by measuring the relationship between the logarithmic ratio of the transmittance of two wavelengths and the value of the scattering influencing factor and transmitting two light beams through the combustion exhaust stream to be measured including the soot aggregate group. The value of the scattering influencing factor corresponding to is determined according to the relationship obtained in advance, and the ratio of the specific scattering coefficient to the specific absorption coefficient in one of the two rays is determined using the determined value of the scattering influencing factor. And a specific attenuation coefficient, which is a coefficient representing the degree to which the light incident on the soot aggregate is attenuated, is calculated based on the calculated ratio and the specific absorption coefficient calculated in advance for one light beam. ratio Since the mass concentration is measured by substituting the attenuation coefficient and the attenuation factor of one light beam into a predetermined calculation formula, the relationship between the scattering influence factor value and the logarithmic ratio of the transmittance of two wavelengths is expressed. By simply calculating the specific absorption coefficient in advance and assuming that the absorption factor is constant, the mass concentration of the soot aggregate in the exhaust stream can be measured easily in consideration of the scattering by the soot aggregate. Can do.
[0016]
According to a fourth aspect of the present invention, in the first or second aspect of the invention, the arithmetic expression is such that the specific attenuation coefficient is σext, the attenuation factor of the one light beam is τ, the mass concentration is Cm, and the light beam is transmitted. When the optical path length is L,
Cm = -lnτ / σext L
Represented by
It exists in the mass concentration measuring method of the soot aggregate in the combustion exhaust gas in any one of Claims 1-3 characterized by the above-mentioned.
[0017]
According to invention of Claim 4, it can measure using the general arithmetic expression of mass concentration.
[0018]
According to a fifth aspect of the present invention, there is provided a transmittance measuring means for measuring the transmittance of each wavelength by transmitting two light beams having different wavelengths to the combustion exhaust stream to be measured including the soot aggregate group, and soot. The storage means that stores in advance the relationship between the logarithmic ratios of the transmittances of the two light beams that have been transmitted through the combustion exhaust stream containing the aggregates, and the measurement by the measurement means. The value of the scattering influence factor corresponding to the logarithmic ratio of the transmittance of the two wavelengths is determined by the relationship stored in the storage means, and the light beam incident on the soot aggregate is determined using the determined value of the scattering influence factor. Is a calculation that calculates the mass concentration by substituting the calculated specific attenuation coefficient and the attenuation factor of the one light beam into a predetermined arithmetic expression. And comprising means That resides in mass concentration measurement apparatus of soot aggregates in the combustion exhaust gas.
[0019]
According to the invention described in claim 4, the transmittance measuring means transmits the two light beams having different wavelengths to the combustion exhaust stream to be measured including the soot aggregate group and measures the transmittance at each wavelength. The storage means stores in advance the relationship between the values of the scattering influencing factors corresponding to the logarithmic ratio of the transmittance of the two light beams transmitted through the combustion exhaust stream containing the soot aggregate group, and the calculation means comprises: For each measurement by the measuring means, the value of the scattering influence factor corresponding to the logarithmic ratio of the measured transmittance of the two wavelengths is determined by the relationship stored in the storage means, and the soot is determined using the determined value of the scattering influence factor. Calculate the specific attenuation coefficient, which is a coefficient representing the degree to which the light incident on the aggregate is attenuated by absorption and scattering, and substitute the calculated specific attenuation coefficient and the attenuation rate of one of the light beams into a predetermined arithmetic expression. Since the concentration is calculated, the claim 1 As in the case of Ming, simply calculating the relationship of the scattering influencing factor value to the logarithmic ratio of the two-wavelength transmittance in advance, and considering the scattering by the soot aggregate, the mass concentration of the soot aggregate in the exhaust stream is simple. Can be measured.
[0020]
According to the sixth aspect of the present invention, the transmittance measuring means includes means for guiding two light beams having different wavelengths to a combustion exhaust stream including a soot aggregate group by coaxializing, and a part of the combustion exhaust stream as a sample. A measurement flow channel, an optical window for incident light along the axial direction of the measurement flow channel, and an optical window for emitting light transmitted through the soot particles in the exhaust are provided. A photodetecting device comprising a measuring optical system, two narrow-band filters for separating two emitted coaxial light beams again, and a photosensor for detecting the intensity of transmitted light that has passed through each filter, and the two wavelengths And a signal processing means for digitally converting the detected light intensity signal and storing the digital data obtained by the conversion, and a computing means for computing the transmittance of each wavelength based on the digital data. Item 5 It consists in mass concentration measurement apparatus of soot aggregates in the combustion exhaust gas.
[0021]
According to the sixth aspect of the present invention, in the transmittance measuring means, the measuring optical system includes means for guiding two light beams having different wavelengths into a combustion exhaust stream containing soot aggregates coaxially formed, and combustion exhaust gas. A measurement channel for sampling a part of the flow, an optical window for entering light along the axial direction of the measurement channel, and an optical for emitting light that has passed through soot particles in the exhaust And a photo-detecting device comprising two narrow-band filters for again separating the two coaxial light beams that have exited and a photosensor that detects the intensity of the transmitted light that has passed through each filter. The calculation means calculates the transmittance of each wavelength based on the digital data accumulated by the signal processing means digitally converting the two-wavelength detected light intensity signals, so that the combustion exhaust flow is not affected. The equivalent to different waves It is transmitted through lead and coaxial the two light rays having, and can detect the intensity of the transmitted light other for calculating the transmittance of the two wavelengths for mass concentration calculation.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the method for measuring the mass concentration of soot aggregates in combustion exhaust according to the present invention will be described in detail with reference to FIG. 1 showing an apparatus for carrying out the method, but before that, the principle of the present invention will be described. .
[0025]
It is known that Bouuguer Lambert's law expressed by the following equation (1) holds for the mass concentration of soot that attenuates light transmission in an atmosphere through which parallel rays pass.
Cm = -lnτ / σext L (1)
In equation (1), τ is the transmittance, L is the optical path length, and σext is the specific attenuation coefficient. Since the transmittance τ is a measured value, and the optical path length L is a value unique to the apparatus, both are easily given. The specific attenuation coefficient σext is a coefficient representing the degree to which the parallel rays incident on the soot aggregate (soot aggregated with several hundred soot elements of about 30 nm diameter) are attenuated. The specific absorption coefficient σabs and the specific scattering are expressed as follows: Expressed as the sum of the coefficients σsca.
σext = σabs + σsca (2)
[0026]
Therefore, in the present invention, the specific absorption coefficient σabs and the specific scattering coefficient σsca are theoretically and experimentally determined, and the mass concentration Cm of the soot is measured based on the theoretical basis. It is improved so that it can be measured easily in real time.
[0027]
Next, the theory of transmitted light attenuation for soot aggregates will be described. When a parallel light beam having a wavelength λ is incident on the soot aggregate group, the transmittance τ is given by the following equation. Here, Io is the incident light intensity, I is the transmitted light intensity, and L is the optical path length.
τ = I / Io = exp (−σextCm L) (3)
σextIs the specific damping coefficient (m²/ Kg), Cm is the mass concentration of soot aggregate (kg / m³⁾The above formula (2) is a logarithmic representation of the formula (3) with respect to Cm. Moreover, Formula (2) is represented like following Formula (4).
[Expression 1]

[0028]
In the above equation (4), E (m) and F (m) are functions of the complex refractive index m, λ is the wavelength, αp = πd / λ, d is the diameter of the soot particle constituting the soot aggregate, and npa is The average value of the number of soot particles constituting the soot aggregate, fn is a factor indicating the distribution width of the size of the soot aggregate, kf is a factor indicating the shape of the soot aggregate, and Df is a fractor indicating the shape of the soot aggregate. Dimension.
The above equation (4) can be rewritten as the following equation.
σext = σabs (1 + ρsa) (5)
In equation (5), ρsa is the ratio of the specific scattering coefficient to the specific absorption coefficient, and is given by the following expression (6).
[Expression 2]

[0029]
From the above equation (6), ρsa is 0 when np is small, and asymptotically approaches a constant value as in the following equation (7) when np is sufficiently large.
[Equation 3]

[0030]
It is known that Df in the above formula (6) is approximately 1.75, and d in α = πd / λ is found to be 30.35 nm from an electron micrograph. When the remaining three unknown parameters are collectively referred to as C (referred to as a scattering influence factor), the following equation (8) is obtained.
[Expression 4]

[0031]
Substituting these values into the above equation (6), further substituting equation (6) into equations (5) and (3), the logarithmic ratio of the transmittances τ1 and τ2 at two wavelengths and the scattering influencing factor C When the relationship is calculated, a graph as shown in FIG. 2 is obtained.
[0032]
For example, if the measured value is lnτ 2 / lnτ 1 = 0.78, C = 5.5 is determined from FIG. When C = 5.5, the relationship between np and ρsa for λ1 = 635 nm and λ2 = 760 nm is calculated as shown in FIG. In the figure, 1.0 on the vertical axis represents the amount of absorption, and one or more portions represent the amount of scattering. The calculation is performed for Kf of 6 and 9. Subscript 1 corresponds to 635 nm, and subscript 2 corresponds to 760 nm.
[0033]
In general, the number of soot particles np is about 200. From FIG. 3, for example, at 635 nm, the ratio ρsa of the specific scattering coefficient to the specific absorption coefficient is 0.19 to 0.20. That is, the ratio of scattering to absorption ρsa in attenuation can be determined from the aggregate theory and the measured transmittance.
[0034]
The specific absorption coefficient σabs is determined by the following procedure so that the soot mass concentration measured by the filter method in steady operation matches the measured value by the transmitted light attenuation method.
[0035]
First, the specific attenuation coefficient σext is determined so that the soot mass concentration measured by the paper filter method during steady operation under typical conditions and the soot mass concentration calculated from the measured value of transmittance at a certain wavelength coincide.
[0036]
Next, at the same time, the transmittances τ1 and τ2 at the two wavelengths λ1 and λ2 are measured during the above-described steady operation, and the value of lnτ2 / lnτ1 obtained from this is substituted into FIG. To decide.
[0037]
If the soot number np = 200 constituting the soot aggregate discharged from a normal diesel engine is applied to FIG. 3 plotted using the scattering influence factor C, the ratio ρsa between the specific scattering coefficient and the specific absorption coefficient is determined. it can.
[0038]
Since there is a relation of σext = σabs (1 + ρsa) shown in the above equation (2), the specific absorption coefficient σabs is determined by substituting the ratio ρsa determined here and the previously determined specific attenuation coefficient σext.
[0039]
Since the specific absorption coefficient σabs is theoretically given by the first term on the right side of the above equation (4), the complex refractive index m = n−ik is obtained by substituting the specific absorption coefficient σabs determined as the wavelength λ into this equation. The function E (m) is determined. According to the conventional research, the value of the complex refractive index m is slightly different depending on the researcher. If the value of E (m) is determined, m corresponding to this value can be determined.
[0040]
The functions E (m) and F (m) are expressed by the following equations (9) and (10).
[Equation 5]

[0041]
As described above, the specific absorption coefficient σabs in the steady operation, the ratio ρsa of the specific scattering coefficient σsca and the specific absorption coefficient σabs are determined, and the specific attenuation coefficient σext is determined, so the transmittance at the wavelength can be measured. The mass concentration Cm can be measured.
[0042]
The value of the specific absorption coefficient σabs during steady operation obtained as described above may be used during transient operation. However, it is affected by the scattering influencing factor C, which is a function of the soot aggregate size distribution, soot aggregate shape, soot aggregate average size, and the like. Therefore, during transient operation, it is necessary to measure lnτ2 / lnτ1 on a real time basis and determine the scattering influence factor C according to the value. By calculating the ratio ρsa of the specific scattering coefficient σsca and the specific absorption coefficient σabs at each time from this C, the specific attenuation coefficient σext at the time of transient operation can be obtained correctly.
[0043]
Returning to FIG. 1, an apparatus for carrying out the method of the present invention will be described. In FIG. 1, a flow path 2 for sampling exhaust gas is provided in the middle or at the outlet of the exhaust pipe 1 of the combustion apparatus, and the sampled exhaust gas is guided to an external measurement flow path 3. One optical window 4 and 5 is provided at each end of the measurement flow path 3 for entering and exiting the light beam. In order to prevent soot from adhering to the optical window and the inner wall of the measurement channel, heating devices 6 and 7 and an air purge device 8 for calibration are attached. Reference numeral 1a denotes a throttle provided in the exhaust pipe 1 so that the sample exhaust can easily enter the measurement channel 3.
[0044]
Two light beams emitted from two

diode lasers

9 and 10 having different wavelengths are coaxially formed by a prism 11. This light beam passes through the beam expander 12 and enters the measurement channel 3 from the optical window 4 and is attenuated by the soot particles and then guided to the detection system through the optical window 5.
[0045]
In the detection system, the two coaxial light beams are divided into two light beams by the beam splitter 13 and then passed through the narrow-band laser filters 14 and 15 so that the two light beams having the laser wavelength of the light source are obtained. To separate. The light intensity of the two light beams is detected by the

photodiodes

16 and 17. The detected analog signal is A / D converted on a real time basis in a signal processing device 18 as a signal processing means, and then stored and stored as digital data. Two sets of digital data strings corresponding to the transmittances of the two wavelengths are transferred to a computing personal computer (personal computer) 19.
[0046]
The personal computer 19 calculates the logarithmic ratio of the transmittance of each wavelength and substitutes this logarithmic ratio into the relational expression calculated based on the optical theory of the soot aggregate beforehand, that is, σsca / σabs at the time of data collection, that is, The value of the ratio ρsa to the specific absorption coefficient to the specific absorption coefficient can be determined. FIG. 2 shows the relationship between the logarithmic ratio of transmittance and the scattering influencing factor C for determining σsca / σabs when 635 nm and 780 nm are used as wavelengths. Further, if the specific attenuation coefficient σext is determined by using the value of C and the specific absorption coefficient σabs obtained separately during steady operation, the measured transmittance value at any one of the two wavelengths λ can be obtained. The mass concentration Cm of soot particles can be calculated by substituting into the above equation (1).
[0047]
In the embodiment described above, a part of the combustion exhaust flow is sampled, two light beams having different wavelengths are incident on the soot particles in the flow coaxially, and the respective transmittances are measured. It can be considered that σsca / σabs is theoretically obtained from the logarithmic ratio of the rate, and further, the mass concentration of the soot is calculated from the measured value of transmittance using σabs obtained by a separate test.
[0048]
Further, in the embodiment, the flow path 2 for sampling the exhaust flow, the optical system incident on the exhaust flow including the soot particles by coaxializing the light of two wavelengths, the measurement flow path 3 through which the light passes, and the two coaxials through which the light passes. An optical / detection system that re-separates the light of each wavelength by wavelength and detects the intensity of each, and a signal processing device 18 that digitizes the obtained analog signal, and a computer 19 that calculates the mass concentration of soot from the digital signal Can be seen as functioning.
[0049]
Furthermore, in the embodiment, the transmittance measuring means for transmitting the two light beams having different wavelengths to the combustion exhaust stream to be measured including the soot aggregate group and measuring the transmittance of each wavelength respectively has different wavelengths. Two

diode lasers

9 and 10, prism 11, measurement channel 3, optical window 4 and optical window 5 as means for guiding the two light beams having the same axis to a combustion exhaust stream including a soot aggregate group. Is provided with a measurement optical system, a light detection device comprising two narrow-

band filters

14 and 15 and

photosensors

16 and 17, a signal processing device 18, and the transmittance of each wavelength based on digital data in advance. It can be seen that this is realized by the personal computer 19 constituting the calculation means for calculating according to the defined program.
[0050]
The storage means for storing in advance the relationship between the values of the scattering influencing factors corresponding to the logarithmic ratio of the transmittance of the two light beams transmitted through the combustion exhaust stream containing the soot aggregate group is not shown in the personal computer 19. 2 is stored in the memory in the form of data, or the relation shown in FIG. 2 is stored in the form of an approximate expression.
[0051]
Further, for each measurement of transmittance, the value of the scattering influence factor corresponding to the logarithmic ratio of the measured transmittance of the two wavelengths is determined by the relationship stored in the storage means, and the value of the determined scattering influence factor is determined. The specific attenuation coefficient, which is a coefficient representing the degree to which the light rays incident on the soot aggregates are attenuated by absorption and scattering, is calculated, and the calculated specific attenuation coefficient and the attenuation factor of one of the light beams are expressed in a predetermined arithmetic expression. The calculating means for substituting and calculating the mass concentration is realized by operating the personal computer 19 according to a predetermined program. In order to calculate the mass concentration, an arithmetic expression into which the specific attenuation coefficient and the light beam attenuation rate are substituted is stored in the memory of the personal computer 19 as part of the program.
[0052]
According to the apparatus of the embodiment described above, the specific absorption coefficient σabs and the specific scattering coefficient σsca are theoretically and experimentally determined, and the accuracy and reliability of the method of measuring the mass concentration Cm of soot from the measurement of the transmittance τ. Can be significantly improved.
[0053]
As for the measurement of the soot particle emission mass concentration (mass in unit volume under standard atmospheric conversion), the conventional method only evaluates the soot concentration in the exhaust gas relative or qualitatively as described above. In contrast, according to the present invention, the mass concentration of soot particles in the exhaust stream can be measured in real time using a simple device based on a theoretical basis.
[0054]
In addition, two diode laser beams having different wavelengths are transmitted through diesel exhaust, and the mass concentration of the soot aggregate is measured quantitatively in real time by the transmitted light attenuation method. Measurement accuracy and reliability can be improved by determining the scattered light influence factor.
[0055]
Further, since the responsiveness is determined by the time required for the exhaust gas to pass through the sample line and the measurement flow path, it has high responsiveness (about 0.2 seconds).
[0056]
Furthermore, since the transmittance, which is a relative value rather than an absolute value of the light intensity, is measured, no calibration is required and the stability is high.
[0057]
Furthermore, by extending the optical path length, 1 mg / m^ThreeIt is possible to measure the low mass concentration of the level.
[0058]
【The invention's effect】
As described above, according to the present invention, the mass concentration of the soot aggregate in the exhaust stream can be easily considered in consideration of scattering by the soot aggregate based on a theoretical basis, or in real time and simply It is possible to provide a method and an apparatus for measuring the mass concentration of soot agglomerates in combustion exhaust gas, which can be measured at the same time.
[Brief description of the drawings]
FIG. 1 is an overall view showing an embodiment of a mass concentration measuring apparatus for soot aggregates for carrying out the method according to the present invention.
FIG. 2 is an example of a diagram for obtaining a scattering influencing factor C for determining σsca / σabs from a logarithmic ratio of transmittances of two wavelengths.
FIG. 3 is a diagram showing an example of the relationship between the number of soot particles np constituting the soot aggregate and the ratio ρsa of the specific scattering coefficient to the specific absorption coefficient.
[Explanation of symbols]
1 Exhaust pipe
2 Dividing flow path
3 Measurement channel
4,5 Optical window
6,7 Heating device
8 Air purge device
9,10 Diode laser
11 Prism
12 Beam expander
13 Beam splitter
14,15 Narrow band laser filter
16, 17 Photodiode
18 Signal processing means (signal processing device)
19 Personal computer (calculation means)

Claims

The relationship between the value of the scattering influencing factor and the logarithmic ratio of the transmittance of two light beams having different wavelengths transmitted through the combustion exhaust stream containing the soot aggregate group is obtained in advance.
The value of the scattering influence factor for the transmittance of each wavelength measured by transmitting the two light beams to the combustion exhaust stream to be measured including the soot aggregate group is determined by the relationship obtained in advance.
Using the determined value of the scattering influence factor, a specific attenuation coefficient, which is a coefficient representing the degree to which the light incident on the soot aggregate is attenuated by absorption and scattering, is calculated,
A method for measuring the mass concentration of soot aggregates in combustion exhaust gas, wherein the calculated specific attenuation coefficient and the attenuation factor of the one light beam are substituted into a predetermined calculation formula to calculate the mass concentration.

The relationship between the logarithmic ratio of the transmittance of two light beams having different wavelengths transmitted through the combustion exhaust stream containing the soot aggregate group and the value of the scattering influence factor corresponding to the logarithmic ratio is obtained in advance.
Measure the transmittance of each wavelength at a predetermined interval by transmitting the two light beams to the combustion exhaust stream to be measured including the soot aggregate group,
For each measurement, the value of the scattering influence factor corresponding to the logarithmic ratio of the measured transmittance of the two wavelengths is determined according to the relationship obtained in advance.
Using the determined value of the scattering influence factor, a specific attenuation coefficient, which is a coefficient representing the degree to which the light incident on the soot aggregate is attenuated by absorption and scattering, is calculated,
A method for measuring the mass concentration of soot aggregates in combustion exhaust gas, wherein the calculated specific attenuation coefficient and the attenuation factor of the one light beam are substituted into a predetermined calculation formula to calculate the mass concentration.

The relationship between the values of the scattering influencing factors corresponding to the logarithmic ratio of the transmittance of two light beams having different wavelengths transmitted through the combustion exhaust stream containing the soot aggregate group is obtained in advance.
The scattering influence factor corresponding to the transmittance of each wavelength measured by transmitting the two light beams to the combustion exhaust stream to be measured including the soot aggregate group is determined by the relationship obtained in advance.
Using the determined value of the scattering influence factor, the ratio of the specific scattering coefficient in one of the two light beams to the specific absorption coefficient is calculated,
By calculating the specific attenuation coefficient, which is a coefficient representing the degree of attenuation of the light incident on the soot aggregate, by the calculated ratio and the specific absorption coefficient calculated in advance for the one light beam,
A method for measuring the mass concentration of soot aggregates in combustion exhaust gas, wherein the calculated specific attenuation coefficient and the attenuation factor of the one light beam are substituted into a predetermined calculation formula to calculate the mass concentration.

When the specific attenuation coefficient is σext, the attenuation factor of the one light beam is τ, the mass concentration is Cm, and the optical path length through which the light beam is transmitted is L,
Cm = -lnτ / σext L
The method for measuring the mass concentration of soot aggregates in combustion exhaust gas according to any one of claims 1 to 3, wherein:

A transmittance measuring means for measuring the transmittance of each wavelength by transmitting two light beams having different wavelengths to the combustion exhaust stream to be measured including the soot aggregate group;
Storage means for storing in advance the relationship between the values of the scattering influencing factors corresponding to the logarithmic ratio of the transmittance of the two light beams transmitted through the combustion exhaust stream containing the soot aggregate group;
For each measurement by the measurement means, a scattering influence factor value corresponding to the logarithmic ratio of the measured transmittance of the two wavelengths is determined by the relationship stored in the storage means, and the determined scattering influence factor value is determined. And calculating a specific attenuation coefficient, which is a coefficient representing the degree to which light rays incident on the soot aggregate are attenuated by absorption and scattering, and calculating the specific attenuation coefficient and the attenuation factor of the one light beam in advance. An apparatus for calculating the mass concentration of soot aggregates in combustion exhaust gas, comprising: a calculating means for calculating the mass concentration by substituting

The transmittance measuring means includes
Means for guiding two light beams having different wavelengths to a combustion exhaust flow including a soot aggregate group coaxially, a measurement flow channel for sampling and flowing a part of the combustion exhaust flow, and an axial direction of the measurement flow channel A measuring optical system having an optical window for incident light along the optical window and an optical window for emitting light transmitted through the soot particles in the exhaust;
A photo-detecting device comprising two narrow-band filters for separating the two coaxial light beams that have exited, and a photosensor that detects the intensity of transmitted light that has passed through each filter;
A signal processing means for digitally converting the detected light intensity signals of the two wavelengths and storing digital data obtained by the conversion;
The apparatus for measuring the mass concentration of soot aggregates in combustion exhaust according to claim 5, further comprising calculating means for calculating the transmittance of each wavelength based on the digital data.