• Energy Research

This work investigates the effects of fuel temperature and injection timing on ammonia direct injection in an optical engine using a multi-hole injector. Flash-boiling may occur over various engine-relevant conditions due to ammonia’s high vapor pressure. This phenomenon impacts spray characteristics and, in severe cases, facilitates cavitation inside the nozzle. Both fuel temperature and injection timing (i.e., ambient conditions during injection) impact the intensity of flash-boiling during fuel injection. Therefore, this work varies fuel temperature (from 320K to 388K) and injection timing (from −60CADaTDC (crank angle degrees after top dead center) to −6CADaTDC) to assess their impact on injection mass flux, discharge coefficients, and macroscopic spray characteristics using an ammonia injection pressure of 200bar. For this purpose, the injection mass is measured by analyzing exhaust gas compositions during engine operation with ammonia injections but without combustion. In addition, diffuse background illumination (DBI) images capture the liquid phase of the fuel spray to characterize spray behavior. The findings reveal that increasing fuel temperature decreases ammonia’s injection mass by up to 12.8% but has little impact on discharge coefficients for late injection timings and high in-cylinder pressures. However, discharge coefficients decrease by up to 17.4% (from 0.58 to 0.48) for early injection timings if fuel temperatures are high. The individual sprays of the 6-hole GDI injector may collapse into a uniform spray at high-density conditions without flash-boiling or under strongly flash-boiling conditions. The findings clarify the impact of ammonia’s high vapor pressure on injection mass and prove the relevance of different spray collapse mechanisms in ammonia direct injection engines.

Ammonia is a promising alternative fuel that can replace current fossil fuels. Hydrogen carrier, zero carbon base emissions, liquid unlike hydrogen, and can be produced using renewable resources, making ammonia a future green fuel for the internal combustion engine. This study aims to show the procedure of utilizing ammonia as a primary fuel with biodiesel in a dual-fuel mode. Hence, a single-cylinder diesel engine was retrofitted to inject ammonia into the intake manifold, and then a pilot dose of biodiesel is sprayed into the cylinder to initiate combustion of the premixed ammonia-air mixture. The effects of various ammonia mass flow rates with a constant biodiesel dose on engine performance and emissions were investigated. Furthermore, a one-dimensional model has been developed to analyze the combustion of ammonia and biodiesel. The results reveal that 69.4% of the biodiesel input energy can be replaced by ammonia but increasing the ammonia mass flow rate slightly decreases the brake thermal efficiency. Moreover, increasing the ammonia load contribution significantly reduced the emissions of CO2, CO, and HC but increased the emission of NO. It was found that ammonia delayed the start of combustion by 2.6CAD compared with pure biodiesel due to the low in-cylinder temperature and the high resistance of ammonia to autoignition. However, the combustion duration of biodiesel/ammonia decreased 19CAD compared with only biodiesel operation at full load, since most of the heat was released during the premixed combustion phase.

Abstract Two energy crops Miscanthus x giganteus and Sida hermaphrodita were used for a phytoremediation study on two different sites of soil contaminated with heavy metals in Poland and Germany. The energy crops were harvested and characterized with regards to fuel properties and thermal decomposition behaviour. Site influences on the data of proximate and ultimate analyses have been observed. Differences in the thermal decomposition are caused by the differences in pH value and heavy metal content of the soils.

AbstractIn the present paper NOx emissions from biomass combustion was studied, with the objective to demonstrate the applicability of stationary computational fluid dynamics simulations, including a detailed representation of the gas phase chemistry, to a multi-fuel lab-scale grate fired reactor using biomass as fuel. In biomass combustion applications, the most significant route for NOx formation is the fuel NOx mechanism. The formation of fuel NOx is very complex and sensitive to fuel composition and combustion conditions. And hence, accurate predictions of fuel NOx formation from biomass combustion rely heavily on the use of chemical kinetics with sufficient level of details. In the present work we use computational fluid dynamics together with three gas phase reaction mechanisms; one detailed mechanism consisting of 81 species and 1401 reactions, and two skeletal mechanisms with 49 and 36 species respectively. Using the detailed mechanism (81 species), the results show a high NOx reduction at a primary excess air ratio of 0.8, comparable to the NOx emission reduction level achieved in the corresponding experiment, demonstrating both the validity of the model and the potential of NOx reduction by staged air combustion.

The CO2 gasification of chars was investigated by thermogravimetric analysis (TGA). The chars were prepared from spruce and its forest residue. Prior to the gasification, the raw materials were pel...

In this paper an online method for automatically reducing complex chemical mechanisms for simulations of combustion phenomena has been developed. The method is based on the Quasi Steady State Assumption (QSSA). In contrast to previous reduction schemes where chemical species are selected only when they are in steady state throughout the whole process, the present method allows for species to be selected at each operating point separately generating an adaptive chemical kinetics. The method is used for calculations of a natural-gas-fueled engine operating under Homogenous Charge Compression Ignition (HCCI) conditions. We discuss criteria for selecting steady state species and the influence of these criteria on the results such as concentration profiles and temperature. (Less)

The thermodynamic analysis carried out focuses on biomass mixing to reduce the formation of corrosive (mainly alkali) chlorides during straw combustion. The calculations confirm the reduction abilities of sewage sludge and peat and provide information on the addition levels at which no corrosive compounds are expected to form. The calculations provide insight into the mechanisms responsible for the disappearance of alkali chlorides. The mechanisms that can potentially take place are known (reaction with sulfur and reaction with or adsorption on aluminosilicates or other ash compounds). However, many aspects remain unclear, and calculations cast light on several of them. The main result obtained in this study is that, in a given binary mixture, the chemical elements involved in the decomposition of corrosive alkali chlorides (or preventing them from forming) change with the mixing proportions, an important fact never mentioned to our knowledge. The practical implications are significant: in a real system, ...

In this study, the influence of various factors on nitrogen oxides (NOx) emissions of a low NOx burner is investigated using a central composite design (CCD) approach to an experimental matrix in order to show the applicability of design of experiments methodology to the combustion field. Four factors have been analyzed in terms of their impact on NOx formation: hydrogen fraction in the fuel (0%–15% mass fraction in hydrogen-enriched methane), amount of excess air (5%–30%), burner head position (20–25 mm from the burner throat) and secondary fuel fraction provided to the burner (0%–6%). The measurements were performed at a constant thermal load equal to 25 kW (calculated based on lower heating value). Response surface methodology and CCD were used to develop a second-degree polynomial regression model of the burner NOx emissions. The significance of the tested factors over their respective ranges has been evaluated using the analysis of variance and by the consideration of the coefficients of the model equation. Results show that hydrogen addition to methane leads to increased NOx emissions in comparison to emissions from pure methane combustion. Hydrogen content in a fuel is the strongest factor affecting NOx emissions among all the factors tested. Lower NOx formation because of increased excess air was observed when the burner was fuelled by pure methane, but this effect diminished for hydrogen-rich fuel mixtures. NOx emissions were slightly reduced when the burner head was shifted closer to the burner outer tube, whereas a secondary fuel stream provided to the burner was found to have no impact on NOx emissions over the investigated range of factors.