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Transition from HCCI to PPC: Investigation of the Effect of Different Injection Timing on Ignition and Combustion Characteristics in an Optical PPC Engine

Lund University-Miao Zhang, Saeed Derafshzan, Leilei Xu, Xue-Song Bai, Mattias Richter, Marcus Lundgren
  • Technical Paper
  • 2020-01-0559
To be published on 2020-04-14 by SAE International in United States
The partially premixed combustion (PPC) concept is regarded as an intermediate process between the thoroughly mixed Homogeneous charge compression ignition (HCCI) combustion and compression ignition (CI) combustion. It’s a combination of auto-ignition mode, a fuel-rich premixed combustion mode, and a diffusion combustion mode. The concept has both high efficiency and low soot emission due to low heat losses and less stratified fuel and air mixtures compared to conventional diesel CI. The mechanisms behind the combustion process are not yet very well known. This work focuses on the efficiency and the in-cylinder process in terms of fuel distribution and the initial phase of the combustion. More specifically, double injection strategies are compared with single injection strategies to achieve different levels of stratification, ranging from HCCI to PPC like combustion as well as poor (43%) to good (49%) of gross indicated efficiency. The experiments were performed in an optical heavy-duty CI engine.To analyze how the efficiency was affected in a transition from HCCI to PPC, the natural luminosity (N.L.) was captured with high-speed video (HSV). To complement…
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Impact of multiple injection strategies on efficiency and combustion characteristics in an optical PPC engine

Lund University-Miao Zhang, Leilei Xu, Saeed Derafshzan, Xue-Song Bai, Mattias Richter, Marcus Lundgren
  • Technical Paper
  • 2020-01-1131
To be published on 2020-04-14 by SAE International in United States
The partially premixed combustion (PPC) concept is regarded as an intermediate process between the fully mixed Homogeneous charge compression ignition (HCCI) combustion and compression ignition (CI) combustion. It is also a combination of auto-ignition mode, a fuel-rich premixed mode, and a diffusion combustion mode. To achieve high efficiency and low soot emission, the in-cylinder mixture process and combustion behavior of PPC are still to be further explored using laser diagnostic. In this paper, a combined combustion deriving from three stages (HCCI stage, transition stage, PPC stage) was achieved by using multiple injection strategies changing from -220° to -8° after top dead center (ATDC) in an optical heavy-duty CI engine. To analyze the interaction between different combustion modes from HCCI, PPC, and CI, the natural luminosity of combustion was captured by high speed camera. The result shows that piston bowl and cylinder wall play an important role on mixture process in the transition stage and PPC stage. Besides, the interaction between different combustion modes result in different ignition behavior, combustion propagation and gross indicated efficiency.

Impact of Octane Number and Injection Timing on Autoignition Behaviour of Gasoline and PRF in PPC

Division of Combustion Engines, Lund University, Lund 22100,-Amir Aziz, Changle Li, Martin Tuner
Division of Fluid Mechanics, Lund University, 221 00 Lund, S-Leilei Xu
  • Technical Paper
  • 2019-01-2167
Published 2019-12-19 by SAE International in United States
Partially premixed combustion (PPC) is one of the advanced combustion concepts that is being actively investigated. A joint experimental and numerical investigations were conducted to explore the effects of octane number and injection timing on the autoignition behaviour with primary reference fuel (PRF) and gasoline fuels under PPC mode in a light-duty DICI engine. In this study, the start of injection (SOI) was selected as the main variable to describe the auto-ignition behaviour of a different fuel. The results revealed that there was a significant difference in autoignition behaviour and combustion characteristics between early and late injection timing. Based on the experimental and numerical results, three difference regimes were defined namely; transition, early SOI PPC and late SOI PPC.
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Effect of Piston Geometry on Stratification Formation in the Transition from HCCI to PPC

Lund University-Changle Li, Xue-Song Bai, Per Tunestal, Martin Tuner
Lund University, Shanghai Jiao Tong University-Leilei Xu
Published 2018-09-10 by SAE International in United States
Partially premixed combustion (PPC) is an advanced combustion strategy that has been proposed to provide higher efficiency and lower emissions than conventional compression ignition, as well as greater controllability than homogeneous charge compression ignition (HCCI). Stratification of the fuel-air mixture is the key to achieving these benefits. The injection strategy, injector-piston geometry design and fuel properties are factors commonly manipulated to adjust the stratification level. In the authors’ previous research, the effects of injection strategy and fuel properties on the stratification formation process were investigated. The results revealed that, for a direct-injection compression ignition engine, by sweeping the injection timing from −180° aTDC (after top dead center) to −20° aTDC, the sweep could be divided into three different regimes: an HCCI regime, a Transition regime and a PPC regime, based on the changing of mixture stratification conditions. When running in the Transition regime, the engine’s efficiency and emissions were poor. Hence, it is optimal to minimize the length of the Transition regime. At the same time, it would be very beneficial to expand the PPC…
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