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ENCIT 2020
18th Brazilian Congress of Thermal Sciences and Engineering
STUDY OF KNOCK OCCURRENCE OF ISOOCTANE AND N-HEPTANE BLENDS IN AN ADAPTED CFR ENGINE
Submission Author:
Ivanir Fischer , PR
Co-Authors:
Ivanir Fischer, Fernando Pereira, Felipe Roman Centeno
Presenter: Ivanir Fischer
doi://10.26678/ABCM.ENCIT2020.CIT20-0745
Abstract
This paper presents the results of an experimental knock investigation performed in an adapted CFR (Cooperative Fuel Research) engine. The tests were performed applying Isooctane (I) and n-Heptane (H) blends at the volumetric percentages: I100H0, I80H20, I60H40, I40H60, I20H80 and I0H100. Each blend was evaluated at different ranges of compression ratio and spark timing. The range depends on the engine operation limits that are established by the knock limit for each fuel. The combustion chamber pressure was measured in bench tests and the knock frequencies were calculated from the pressure signal. Using a band pass filter, the knock pressure oscillation was detected and a knock factor was calculated by both, the Stochastic Knock Detection (SKD) and the Knock Intensity (KI) methods. For each fuel blend and compression ratio, the spark timing was increased until achieve audible knock condition. For each condition, the combustion chamber pressure was measured for 200 consecutive cycles. The results showed that the SKD method was more effective to quantify the knock intensity, as it simultaneously considers the intensity in each cycle and the knock recurrence over the cycles.
Keywords
Knock, Isooctane, N-heptane, CFR, SKD
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