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Research Papers: Fuel Combustion

J. Energy Resour. Technol. 2018;140(10):102201-102201-17. doi:10.1115/1.4039745.

Fuel injection parameters such as fuel injection pressure (FIP) and start of main injection (SoMI) timings significantly affect the performance and emission characteristics of a common rail direct injection (CRDI) diesel engine. In this study, a state-of-the-art single cylinder research engine was used to investigate the effects of fuel injection parameters on combustion, performance, emission characteristics, and particulates and their morphology. The experiments were carried out at three FIPs (400, 700, and 1000 bar) and four SoMI timings (4 deg, 6 deg, 8 deg, and 10 deg bTDC) for biodiesel blends [B20 (20% v/v biodiesel and 80% v/v diesel) and B40 (40% v/v biodiesel and 60% v/v diesel)] compared to baseline mineral diesel. The experiments were performed at a constant engine speed (1500 rpm), without pilot injection and exhaust gas recirculation (EGR). The experimental results showed that FIP and SoMI timings affected the in-cylinder pressure and the heat release rate (HRR), significantly. At higher FIPs, the biodiesel blends resulted in slightly higher rate of pressure rise (RoPR) and combustion noise compared to baseline mineral diesel. All the test fuels showed relatively shorter combustion duration at higher FIPs and advanced SoMI timings. The biodiesel blends showed slightly higher NOx and smoke opacity compared to baseline mineral diesel. Lower particulate number concentration at higher FIPs was observed for all the test fuels. However, biodiesel blends showed emission of relatively higher number of particulates compared to baseline mineral diesel. Significantly lower trace metals in the particulates emitted from biodiesel blend fueled engine was an important finding of this study. The particulate morphology showed relatively smaller number of primary particles in particulate clusters from biodiesel exhaust, which resulted in relatively lower toxicity, rendering biodiesel to be more environmentally benign.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(10):102202-102202-10. doi:10.1115/1.4040010.

Gasoline compression ignition (GCI) offers the potential to reduce criteria pollutants while achieving high fuel efficiency. This study aims to investigate the fuel chemical and physical properties effects on GCI operation in a heavy-duty diesel engine through closed-cycle, three-dimensional (3D) computational fluid dynamic (CFD) combustion simulations, investigating both mixing-controlled combustion (MCC) at 18.9 compression ratio (CR) and partially premixed combustion (PPC) at 17.3 CR. For this work, fuel chemical properties were studied in terms of the primary reference fuel (PRF) number (0–91) and the octane sensitivity (0–6) while using a fixed fuel physical surrogate. For the fuel physical properties effects investigation, six physical properties were individually perturbed, varying from the gasoline to the diesel range. Combustion simulations were carried out at 1375 RPM and 10 bar brake specific mean pressure (BMEP). Reducing fuel reactivity was found to influence ignition delay time (IDT) more significantly for PPC than for MCC. 0D IDT calculations suggested that the fuel reactivity impact on IDT diminished with an increase in temperature. Moreover, higher reactivity gasolines exhibited stronger negative coefficient (NTC) behavior and their IDTs showed less sensitivity to temperature change. In addition, increasing octane sensitivity was observed to result in higher fuel reactivity and shorter IDT. Under both MCC and PPC, all six physical properties showed little impact on global combustion behavior, NOx, and fuel efficiency. Among the physical properties investigated, only density showed a notable effect on soot emissions. Increasing density led to higher soot due to deteriorated air entrainment into the spray and the slower fuel-air mixing process.

Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Engineering

J. Energy Resour. Technol. 2018;140(10):102901-102901-11. doi:10.1115/1.4039981.

The phenomenon of liquefied natural gas (LNG) cargo weathering is considered in terms of the conditions influencing boil-off gas (BOG) rates during the offshore movements and handling of LNG on marine LNG carriers (LNGC), floating storage and regasification unit (FSRU), and floating storage units (FSU). The range of compositions (grades) of commercially traded LNG is significantly broader than the range of compositional changes caused by typical storage times for offshore LNG cargoes. The different nitrogen and natural gas–liquid concentrations of LNG cargoes (i.e., ethane and heavier C2+ components) significantly influence the impacts of weathering and ultimately determine whether the LNG delivered to customers is within sales specifications or not. The BOG from LNG in storage is richer in methane and nitrogen; if nitrogen is present in the LNG, otherwise just richer in methane, than the LNG from which it is derived. This leads to the LNG becoming richer in the C2+ components as ageing progresses. LNG weathering is shown not to play a significant role in the rollover phenomenon of LNG moved and stored offshore, because nitrogen contents are low (typically < 1.0%) and auto-stratification is rarely an issue. LNG stored for long periods on FSU (greater than 8 weeks, or so) experiences significant weathering effects, but most LNG processed by FSRU (and most FSU) has a residence time of less than 30 days or so, in which case weathering has only minor operational impacts. Weathering rates and LNG compositional changes on FSRU for different LNG grades are provided.

Commentary by Dr. Valentin Fuster

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