KAUST DepartmentClean Combustion Research Center
Mechanical Engineering Program
Physical Science and Engineering (PSE) Division
Permanent link to this recordhttp://hdl.handle.net/10754/625548
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AbstractThis chapter discusses the combustion processes and the link to the fuel properties that are suitable for them. It describes the basic three concepts, including spark ignition (SI) and compression ignition (CI), and homogeneous charge compression ignition (HCCI). The fuel used in a CI engine is vastly different from that in an SI engine. In an SI engine, the fuel should sustain high pressure and temperature without autoignition. Apart from the dominating SI and CI engines, it is also possible to operate with a type of combustion: autoignition. With HCCI, the fuel and air are fully premixed before combustion as in the SI engine, but combustion is started by the increased pressure and temperature during the compression stroke. Apart from the three combustion processes, there are also a few combined or intermediate concepts, such as Spark-Assisted Compression Ignition (SACI). Those concepts are discussed in terms of the requirements of fuel properties.
CitationJohansson B (2016) Fuels and Combustion. Biofuels from Lignocellulosic Biomass: 1–27. Available: http://dx.doi.org/10.1002/9783527685318.ch1.
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Homogeneous Charge Compression Ignition (HCCI) and Partially Premixed Combustion (PPC) in Compression Ignition Engine with Low Octane GasolineAn, Yanzhao; Jaasim, Mohammed; Raman, Vallinayagam; Hernandez Perez, Francisco; Im, Hong G.; Johansson, Bengt (Energy, Elsevier BV, 2018-06-11) [Article]The present study investigated the in-cylinder combustion for low octane 70 primary reference fuel (PRF70) by the method of the flame index during the transition from homogeneous charge compression ignition (HCCI) combustion to partially premixed combustion (PPC). Full cycle engine simulations were performed using CONVERGE™, coupled with chemical kinetics. Good agreements between the simulations and experiments were achieved at HCCI and PPC combustion modes. The fully premixed HCCI mode was achieved at the earliest injection timing of −180 CAD aTDC with the combustion temperature below 1600 K, where the formation of soot and NOx can be successfully avoided. For the injection timing of −100 CAD aTDC, the premixed charge compression ignition (PCCI) was achieved where the premixed combustion clouds were mainly distributed in the piston top-land zone and were surrounded by the diffused combustion that occurs in the piston bowl and the periphery of piston top. Less premixed flames were formed in piston top and surrounded by more diffusion mixtures at PPC mode. The in-cylinder HO evolution profile displayed two bumps which were distributed in low temperature zone and high temperature zone respectively. The spatial and temporal evolution of HO is very similar to the distribution of premixed flames.
Ignition delay measurements of a low-octane gasoline blend, designed for gasoline compression ignition (GCI) enginesAlAbbad, Mohammed A.; Badra, Jihad; Djebbi, Khalil; Farooq, Aamir (Proceedings of the Combustion Institute, Elsevier BV, 2018-06-21) [Article]A blend of low-octane (light and heavy naphtha) and high-octane (reformate) distillate fuels has been proposed for powering gasoline compression ignition (GCI) engines. The formulated 'GCI blend' has a research octane number (RON) of 77 and a motor octane number (MON) of 73.9. In addition to ~64 mole% paraffinic components, the blend contains ~20 mole% aromatics and ~15 mole% naphthenes. Experimental and modeling studies have been conducted in this work to assess autoignition characteristics of the GCI blend. Ignition delay times were measured in a shock tube and a rapid comparison machine over wide ranges of experimental conditions (20 and 40 bar, 640-1175 K, ϕ = 0.5, 1 and 2). Reactivity of the GCI blend was compared with experimental measurements of two surrogates: a multi-component surrogate (MCS) and a two-component primary reference fuel (PRF 77). Both surrogates capture the reactivity of the fuel quite well at high and intermediate temperatures. The MCS does a better job of emulating the fuel reactivity at low temperatures, where PRF 77 is more reactive than the GCI blend. Ignition delay times of the two surrogates are also simulated using detailed chemical kinetic models, and the simulations agree well with the experimental findings. The results of rate-of-production analyses show important role of cycloalkane chemistry in the overall autoignition behavior of the fuel at low temperatures.
Compression Ratio and Intake Air Temperature Effect on the Fuel Flexibility of Compression Ignition EngineAlRamadan, Abdullah; Ben Houidi, Moez; Aljohani, Bassam S.E.; Eid, Hassan; Johansson, Bengt (SAE International, 2019-09-10) [Conference Paper]The effect of compression ratio (CR) and intake air temperature on the combustion characteristics of fuels with different octane ratings were investigated on a single-cylinder heavy duty engine. The study focused on Primary Reference Fuels (PRFs) and commercial grade diesel with octane numbers ranging from 0 to 100. The engine was configured at a CR of 11.5:1, which is lower than typical heavy-duty compression ignition CI engines. This aims to compare the fuels' burning regime with recently reported measurements at CR17:1. Experiments were performed at different intake air temperatures of 20 to 80 °C and net indicated mean effective pressure (IMEPNet) of 5 to 20 bar. The injection rates have been characterized to determine the hydraulic delay of the injector and thus define the actual ignition delay time. At low loads, diesel-like fuels were found to burn in partially premixed combustion (PPC) mode whereas high octane fuels did not ignite. At high loads, fuels combustion becomes diffusion driven regardless of their RON or MON values. The effect of intake air temperature on the combustion characteristics depended on the combination of the octane ratings and the engine load. At high loads, fuels with low octane numbers were insensitive to the change of the intake air temperature. The ignition delay time was short enough to maintain a diffusion driven combustion. At lower loads, it is more challenging to reach conditions where the combustion characteristics are invariant regardless of the fuel's RON and MON values (Fuel Flexible). At the low tested compression ratio of 11.5:1, the extent of fuel flexibility is limited to only high loads (IMEPNet = 20 bar) whereas it is extended to intermediate loads (IMEPNet = 10 and 15 bar) at CR17:1.