Combustion Stratification for Naphtha from CI Combustion to PPC

Abstract

This study demonstrates the combustion stratification from conventional compression ignition (CI) combustion to partially premixed combustion (PPC). Experiments are performed in an optical CI engine at a speed of 1200 rpm for diesel and naphtha (RON = 46). The motored pressure at TDC is maintained at 35 bar and fuelMEP is kept constant at 5.1 bar to account for the difference in fuel properties between naphtha and diesel. Single injection strategy is employed and the fuel is injected at a pressure of 800 bar. Photron FASTCAM SA4 that captures in-cylinder combustion at the rate of 10000 frames per second is employed. The captured high speed video is processed to study the combustion homogeneity based on an algorithm reported in previous studies.Starting from late fuel injection timings, combustion stratification is investigated by advancing the fuel injection timings. For late start of injection (SOI), a direct link between SOI and combustion phasing is noticed. At early SOI, combustion phasing depends on both intake air temperature and SOI. In order to match the combustion phasing (CA50) of diesel, the intake air temperature is increased to 90°C for naphtha. The combustion stratification from CI to PPC is also investigated for various level of dilution by displacing oxygen with nitrogen in the intake. The start of combustion (SOC) was delayed with the increase in dilution and to compensate for this, the intake air temperature is increased. The mixture homogeneity is enhanced for higher dilution due to longer ignition delay. The results show that high speed image is initially blue and then turned yellow, indicating soot formation and oxidation. The luminosity of combustion images decreases with early SOI and increased dilution. The images are processed to generate the level of stratification based on the image intensity. The level of stratification is same for diesel and naphtha at various SOI. When O 2 concentration in the intake is decreased to 17.7% and 14.7%, stratification level is decreased. NO X emission for both diesel and naphtha show a decreasing trend from CI to PPC.Comparing diesel and naphtha, the soot emission is lower for naphtha. NO X and soot emissions at various SOI are correlated with high speed images of combustion to explain the combustion stratification.

Implementation of thermal and fuel stratification strategies to extend the load limit of HCCI engine

“…Early injection timing causes high PRR and Knock, while late DI results in high NOX emission (Dev et al 2018). For high load operation SCCI uses similar strategies to PCCI to achieve very high load operations with limiting emissions (Dev et al 2018;Vallinayagam et al 2017). The various strategies to extend the SCCI load limit are 1.…”

“…The various strategies to extend the SCCI load limit are 1. Lowering CR and increasing intake pressure boost (Dec, Dernotte, and Ji 2017;Vallinayagam et al 2017). 2.…”

“…The strategy adopts the fuel injection in two ways. 1) 100% fuel is directly injected into the cylinder, the DI is later than HCCI and earlier than conventional CI during an engine cycle, is called direct injection fuel or mixture stratification (Krisman et al 2012;Lu et al 2008; Berntsson Table 1 Comparison between SI, CI, HCCI, PCCI, RCCI and SCCI (Vallinayagam et al 2017;Benajes et al 2014;Ma et al 2013;Nieman et al 2012;Krisman et al 2012;Dec et al 2011;Yang et al 2011aYang et al , 2011bLu et al 2008;Sjöberg and Dec 2004, 2007aBerntsson and Denbratt 2007;Hwang et al 2007;Lee 2006, 2007;Kanda et al 2005;Nakagome et al 1997;Ganesan 1994;Heywood 1988 In-cylinder stratification ----------------- Lee 2006Lee , 2007Dec 2004, 2007a). Depending on the injection timings for gasoline fuel, the levels of stratifications are defined as follows (Dempsey et al 2016);…”

Combustion-Based Transportation in a Carbon-Constrained World—A Review

“…These Low-Temperature Combustion (LTC) concepts reduce the local flame temperature and equivalence ratio in such a way that NO x and soot formation are reduced simultaneously. When the Start of Injection (SOI) is advanced from late to early fuel injection timings, combustion drifts from CI toward HCCI condition (Vallinayagam et al 2017).…”

Combustion stratification study of partially premixed combustion using Fourier transform analysis of OH* chemiluminescence images

“…However, the results of the stratification definition used there (see ''Angular, radial and vertical stratification'' section below for more detail) were significantly affected by noise, and it was hard to compare the stratification level of different PPC points objectively. Recently, the angular stratification method was applied by Vallinayagam et al 16 to study the combustion stratification for Naphtha ranging from CI combustion to PPC. Their results showed a strong correlation between combustion stratification and NOx/soot emissions as shown in Figure 1.…”