Multiple fuel injection strategy for premixed charge compression ignition combustion engine using biodiesel blends

In the last decade, advanced combustion techniques of the low-temperature combustion (LTC) family have attracted researchers because of their excellent emission characteristics; however, combustion control remains the main issue for the LTC modes. The objective of this study was to explore premixed charge compression ignition (PCCI) combustion mode using a double pilot injection (DPI; pilot-pilot-main) strategy to achieve superior combustion control and to tackle the soot-oxides of nitrogen (NOx) trade-off. Experiments were carried out in a single-cylinder research engine fueled with 20% v/v biodiesel blended with mineral diesel (B20) and 40% v/v biodiesel blended with mineral diesel (B40) vis-à-vis baseline mineral diesel. Engine speed and rate of fuel-mass injected were maintained constant at 1500 rpm and 0.6 kg/h mineral diesel equivalent, respectively. Pilot injection timings (at 45° and 35° before top dead center (bTDC)) and fuel quantities were fixed, while three fuel injection pressures (FIPs) and four different start of the main injection (SoMI) timings were investigated in this study. Results showed that multiple pilot injections resulted in a stable PCCI combustion mode, making it suitable for higher engine loads. For all test fuels, advancing SoMI timings led to relatively lesser knocking; however, engine performance characteristics degraded at advanced SoMI timings. B40 exhibited relatively superior engine performance among different test fuels at lower FIP; however, the difference in engine performance was insignificant at higher FIPs. Fuel injection parameters showed a significant effect on emissions, especially on the NOx and particulates. Advancing SoMI timing resulted in 20%–50% lower particulates emissions with a slight NOx increase; however, the differences in emissions at different SoMI timings reduced at higher FIPs. Somewhat higher particulates from biodiesel blends were a critical observation of this study, which was more dominant at advanced SoMI timings. Qualitative correlation between NOx-total particulate mass (TPM) was another critical analysis, which exhibited the relative importance of different fuel injection parameters for other alternative fuels. Overall, B20 at 700 bar FIP and 20° SoMI timing emerged as the most promising proposition with some penalty in CO emission.

Studying the causes of destruction of steam superheater tubes in boiler equipment

Results of comprehensive studies of samples of prematurely destroyed 57×4 mm steam superheaer tubes of STBA 22 steel used in a boiler unit of Singburi Sugar Co, Ltd factory (Thailand) are presented. The tubes were manufactured at Interpipe Niko Tube Ltd. (Ukraine) according to JIS G 3462 Standard (Japan). They were destroyed in a short (~240 hrs) term of operation. The cause of premature destruction of tubes of the above steel grade and size assortment in the boiler unit has been established. Based on present-day investigation methods (metallography, X-ray diffraction, etc.), it was found that the tubes were operated with violation of fuel combustion conditions and heat-carrying agent circulation. Characteristic features of operation of damaged tubes include high thermal stresses from the side of the fire-chamber and limitation (or absence) of circulation of the heat-carrying agent (blockage in bends, drum heads, etc.). During operation, the tubes were also exposed to significant thermal vibration stresses (unstable combustion conditions). Prolonged overheating occurred at temperatures above 1000 °C because of violation of circulation of heat-carrying agent and unstable combustion mode. High thermal stresses at almost complete absence of a heat-carrying agent, uneven distribution of growing heat flows caused by violation of the combustion mode in the fire-chamber contributed to accelerated degradation of structure and thermal destruction of the tube metal. In a short term of operation (~240 hours), there was a significant change in the tube size (accelerated high-temperature creep) and complete recrystallization of metal structure throughout the entire wall thickness of the damaged tubes. It has been established that the accelerated degradation of metal microstructure in the destroyed tubes was associated with both overheating of the tube wall and the as-delivered metal structure non-recommended for operation at high temperatures and pressures. It was shown that it is necessary to adjust the heat treatment conditions for these tubes at Interpipe Niko Tube Ltd. The study results have made it possible to develop recommendations for eliminating violations of operating conditions and establishing control of actual heat flows in the most thermally loaded sections of the Singburi Sugar Co. Ltd factory’s steam boiler superheater. Taking into account peculiarities of the boiler equipment and its operating conditions, it was also recommended to use a more heat-resistant and refractory steel instead of the currently used material for manufacture of the steam superheater tubes. Keywords: boiler tube, steam superheater, damage, thermal destruction, structure degradation, combustion conditions, heat carrier circulation, overheating.

Performance, combustion, and emission evaluation of ethanol-gasoline blends ignited by diesel in dual-fuel intelligent charge compression ignition (ICCI) engine

A recent proposed dual-fuel combustion mode, intelligent charge compression ignition (ICCI), realizes the high-efficiency and clean combustion by organizing continuous stratification in a wide range of engine load. The paper investigated the performance of alcohol blended gasoline as low reactivity fuel (LRF) in ICCI combustion mode. Pure ethanol named E100 was also tested as LRF for comparison. To emphasize the differences of LRF properties and exclude the effect of the heat release phasing, the diesel injection timing was adjusted to maintain the same combustion phasing (CA50) at various LRF ratios under medium load. The results showed that E100 and E85 (ethanol ratio in gasoline-ethanol blend) promoted the degree of homogeneous combustion and eradicated soot emissions despite a slight increase of NOx. The maximum indicated thermal efficiency (ITE) was over 51.1% using E85, followed by 50.5% of E50. The perfect substitution ratio at the maximum ITE decreased from more than 80% to about 65% when increasing the ethanol ratio in LRF from 10% to 100%. The unregulated emissions such as aldehydes, ethylene, and methane, produced from incomplete combustion of ethanol were inhabited by E85, while the formation of toluene attributed to the appropriate carbon chain length of gasoline diminished when using E85 and E100.

Feasibility Study of Bio-fuel As a Sustainable Product of Biomass: An Overview of Its Fundamentals, Application and Environmental Impact

The energy crisis and ecological disasters have become a critical problem in recent decades. The human activities through industrial operations increase emissions and other pollutant particulates in the world as a result of steady patronage on fossil feedstock. Several experiments were performed to identify an alternative fuel meeting the rising energy demand. Biomass (bio-fuel) has recently been developed as an economical fuel, environmentally friendly resource, renewable and sustainable fuel. Approximately 350 crop plants were evaluated and some of them could be considered as suitable alternative diesel engine fuels. To increase the bio-fuel quantity globally, apart from crops, other biomaterial sources are considered potential in biofuel production. It was shown that the properties of biofuel combustion are identical to fossil. In the experimental combustion of biodiesel blends, higher ignition pressure and temperature, shorter ignition delay, and higher peak release were recorded. This paper is a literature review on the need for biofuels as a global renewable fuel resource and aims to explain the characteristics of combustion and pollutant formation in the application of biofuels. The study also stated the resources, the use of biogas and its emission impact in flameless combustion mode. With holistic adoption of biomass source of fuel together with the modern conversion techniques, issues from fuel emissions will be mitigated.

Numerical investigation of fuel flexibility in a small-scale flameless combustor

Numerical simulation of a laboratory flameless combustor was performed to investigate the flexibility to burn alternative fuels to natural gas. The studied fuels are biogas, syngas and a mixture of ammonia and methane. The inlet temperatures of air and fuel, the equivalence ratio and the geometrical characteristics of the combustor were maintained constant. The results show that flameless combustion is observed in the biogas and in the NH3/CH4 mixture, while the syngas burns according to the conventional non-premixed combustion mode. According to the predictions, the biogas emits 1.1 ppm of NOx and 229 ppm of CO, syngas produces 7.8 ppm of NOx and 35 ppm of CO and the NH3/CH4 mixture emits about 3900 ppm of NOx and 608 ppm of CO. The high NOx and CO emissions in the NH3/CH4 mixture show that the combustor needs to be optimized to burn a nitrogen-containing fuel.