Analiza uticaja kalibracije protokomera za gas na tačnost određivanja emisije čestica dizel motora

Abstract

U radu je prikazan računski postupak za procenu greške određivanja masenog stepena razblaženja uzorka izduvnog gasa i njegovog uticaja na tačnost određivanja ekvivalentnog masenog protoka izduvnog gasa. Na osnovu toga analizirane su tri metode pojedinačne kalibracije masenih termalnih protokomera za gas. Analiza pokazuje da bez obzira na primenjeni princip kalibracije, direktna primena preporuka Pravilnika ECE R49 u domenu određivanja srednjeg masenog stepena razblaženja dovodi do greške u rasponu od ±0.5÷11.0 %, što metodu čini neprihvatljivom. Daljom analizom je obuhvaćena posebna tehnika diferencijalne kalibracije instrumenata za merenje ukupnog protoka razblaženog uzorka gasa i protoka vazduha za razblaženje, čijom se primenom, prema dobijenim rezultatima, greška određivanja srednjeg masenog stepena razblaženja može svesti u granice od 0.2÷0.8 %, dok se greška ekvivalentnog masenog protoka izduvnog gasa zavisno od protoka, kreće u dozvoljenim granicama od 1.1÷1.9 %.

A numeric procedure for the estimation of the accuracy of diesel engine particulate emission measurement has been presented in this paper. The analysis has been provided for mass dilution ratio (DRmass) and equivalent exhaust mass flow (GEDF) regarding the particulate emission measurement based on gravimetric principle with the Partial-Flow Dilution System with heated micro-tunnel and particulate Total Sampling (PFDS-TS Type, accord. to ECE R.49 and ISO 8178). The analysis has been applied to the measurement of the air dilution (GDIL) and total diluted gas sample (GTOT) mass flows provided by means of thermal mass flow meters. Three basic flow meters calibration principles have been analyzed too. According to the results, the recommendations from ECE R49, if strictly applied, lead to the mass dilution ratio error of ±0.5÷11.0 %, which is much beyond proposed limits, making this method unacceptable. The thermal mass flow meters differential calibration procedure has been analyzed, and as a result, increased accuracy of mass dilution ratio (0.2÷0.8 %) and that of equivalent exhaust mass flow (1.1÷1.9 %) has been reported.