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In this paper, the soot-NOx trade-off and fuel efficiency of various aromatic oxygenates is investigated in a modern DAF heavy-duty diesel engine. All oxygenates were blended to diesel fuel such that the blend oxygen concentration was 2.59 wt.-%. The oxygenates in question, anisole, benzyl alcohol and 2-phenyl ethanol, have similar heating values and cetane numbers, but differ in the position of the functional oxygen group relative to the aromatic ring. The motivation for this study is that in lignin, a widely available and low-cost biomass feedstock, similar aromatic structures are found with varying position of the oxygen group to the aromatic ring. From the results it becomes clear that both the soot-NOx trade-off and the volumetric fuel economy (i.e. ml/kWh) is improved for all oxygenates in all investigated work points.

Numerous previous studies have reported that the reduction of emissions by adapting oxygenated bio-fuels chiefly depend on the overall oxygen percentage of the blended oxygenates. However, the effect of molecular structures of the fuels has sometimes only been attributed to differences in auto-ignition quality (i.e. cetane number). In this paper, fuels with two kinds of molecular structures, namely linear and cyclic, have been studied. It reports on emissions tests on a modified in-line 6-cylinder DAF HD Diesel engine with several selected oxygenates mixed with diesel. Fuels in question here are from the non-oxygenates group: n-hexane and cyclohexane, and the oxygenate group: 1-hexanol and cyclohexanol. In order to isolate the effect of molecular structure, the blend compositions are chosen such that the overall oxygen fraction of all blends is the same.

Lignocellulosic biomass consists of (hemi-) cellulose and lignin. Accordingly, an integrated biorefinery will seek to valorize both streams into higher value fuels and chemicals. To this end, this study evaluated the overall combustion performance of both cellulose- and lignin derivatives, namely the high cetane number (CN) di-n-butyl ether (DnBE) and low CN anisole, respectively. Said compounds were blended both separately and together with EN590 diesel. Experiments were conducted in a single cylinder compression ignition engine, which has been optimized for improved combustion characteristics with respect to low emission levels and at the same time high fuel efficiency. The selected operating conditions have been adopted from previous “Tailor-Made Fuels from Biomass (TMFB)” work.

Gasoline direct injection engines can greatly improve the fuel economy, but the idea mixture distribution cannot be easily controlled. In this paper, the linearized instability sheet atomization (LISA) and large eddy simulation (LES) implemented into KIVA-3V code were used to study the gasoline hollow cone spray process for gasoline direct injection (GDI) in a constant volume vessel. The three-dimensional results show that the LISA model can effectively simulate the gasoline hollow cone spray and obtain the string structure compared to the experiment data. And the velocity interpolation method can reduce the grid dependency of spray simulation. Using dense grid (about 8 million cells) in LES and RANS all can obtain the good spray tip penetration and width. Unlike diesel spray, for gasoline spray there are not big difference between the results using LES and RANS. In additional the ambient pressure significantly influence the gasoline spray shape.

Ambient pressure and temperature are two main factors affecting the engine performance. As altitude increases, the air volume and air temperature entering the cylinder per cycle decrease due to the lowering of atmospheric pressure and temperature, which directly affects the engine performance. As a result, engine performance in the plateau environment degrades while the power, economy, and emission performance of the engine significantly deteriorate. This paper focuses on the simulation and parameter optimization of the combustion process of non-road methanol engines, and 1D simulation is for BSFC (Brake Specific Fuel Consumption) prediction while 3D simulation is for soot and NOx (Nitrogen Oxides) predictions. Discusses, analyzes and predicts the feasibility of non-road methanol engines for high altitude conditions. Especially the application of high proportion of methanol in non-road methanol engines at high altitudes.

In the present study, an improved multi-dimensional CFD code has been used to simulate the mixture formation and combustion process of a DI diesel engine. WAVE breakup model constants C0 and C1 are modified according to a linear expression, which is a function relation to the gas pressure in-cylinder. Reasonable agreements of the measured and simulated data of in-cylinder pressure, mean temperature, NOx and soot emissions were achieved for different engine operation conditions. At the same time, the effects of different spray angles on the diesel engine mixture formation and combustion have been further simulated based on the improved multi-dimensional fuel spray and combustion models. The influence of different testing conditions mentioned above on the PM and gaseous pollutant was also discussed in this paper. Predicted trends of soot and NOx formation are also presented together with the corresponding measured data.

Detailed chemical kinetics is essential for accurate prediction of combustion performance as well as emissions in practical combustion engines. However, implementation of that is challenging. In this work, dynamic adaptive chemistry (DAC) is integrated into large eddy simulations (LES) of an n-heptane spray flame in a constant volume chamber (CVC) with realistic application conditions. DAC accelerates the time integration of the governing ordinary differential equations (ODEs) for chemical kinetics through the use of locally (spatially and temporally) valid skeletal mechanisms. Instantaneous flame structures and global combustion characteristics such as ignition delay time, flame lift-off length (LOL) and emissions are investigated to assess the effect of DAC on LES-DAC results. The study reveals that in LES-DAC simulations, the auto-ignition time and LOL obtain a well agreement with experiment data under different oxygen concentrations.

Mixing is inhibited both by the relatively low volatility of conventional diesel fuel and the short premixing time due to high fuel reactivity (i.e. cetane number (CN)). Consequently, in this research two promising oxygenates which can be produced from 2nd generation biomass -ethanol from cellulose and anisole from lignin - will be blended to gasoline, further doped with ignition improver. This will result in a diesel-like CN, but with a higher gasoline-like volatility. There is, however, also a more practical motivation for this study. In Europe, the dieselization trend is resulted in a growing excess of gasoline, which is currently largely exported to the USA at additional transport costs. Boosting the cetane number of gasoline into the diesel range with ignition improvers is a promising route to more efficiently consume European refinery products within Europe.

This study presents a detailed experimental investigation on the cycle-by-cycle variations in a natural gas/diesel dual fuel engine with EGR. The experiment used a single-cylinder, four-stroke, water-cooled, DI diesel engine. The EGR ratio, diesel injection timing and pilot diesel quantity were varied respectively while all the other parameters were held constant. The parameters of cylinder pressure are used to investigate the cyclic variations. The results show that the cylinder peak pressure, the maximum rate of pressure rise and the indicated mean effective pressure decrease. COVimep increases to 18.9% with 25% EGR ratio. The interdependency between the pressure parameters and their corresponding crank angles become weak with the increasing EGR ratio. The increasing EGR ratio increases the ignition delay. The cylinder peak pressure and the maximum rate of pressure rise increase dramatically with the advance of the pilot diesel injection timing.

In earlier research, a new class of bio-fuels, so-called cyclic oxygenates, was reported to have a favorable impact on the soot-NOx trade-off experience in diesel engines. In this paper, the soot-NOx trade-off is compared for two types of cyclic oxygenates. 2-phenyl ethanol has an aromatic and cyclohexane ethanol a saturated or aliphatic ring structure. Accordingly, the research is focused on the effect of aromaticity on the aforementioned emissions trade-off. This research is relevant because, starting from lignin, a biomass component with a complex poly-aromatic structure, the production of 2-phenyl ethanol requires less hydrogen and can therefore be produced at lower cost than is the case for cyclohexane ethanol.

Turbulent jet ignition (TJI) has the advantages of improving burning rates and expanding lean burn limitations of gasoline engines. Based on a single cylinder engine, combustion process with different ignition methods, including single spark ignition, twin spark ignition, one-hole TJI and seven-hole TJI, are studied in this work. Experiments are carried out under conditions with different air/fuel equivalence ratios and different engine loads. Results show that the cycle-to-cycle variations of TJI combustion, which is evaluated by coefficient of variations (CoV) of IMEP and CoV of peak pressure, are obviously reduced due to the fast burning rate induced by the jet flame, and one-hole TJI combustion has the best combustion stability, especially for reducing the CoV of peak pressure.

Strategies to suppress knock have been extensively investigated to pursue thermal efficiency limits in downsized engines with a direct-injection spark ignition. Comprehensive considerations were given in this work, including the effects of second injection timing and injector location on knock combustion in a downsized gasoline engine by large eddy simulation. The turbulent flame propagation is determined by an improved G-equation turbulent combustion model, and the detailed chemistry mechanism of a primary reference fuel is employed to observe the detailed reaction process in the end-gas auto-ignition process. The conclusions were obtained by comparing the data to the baseline single-injection case with moderate knock intensity. Results reveal that for both arrangements of injectors, turbulence intensity is improved as the injecting timing is retarded, increasing the flame propagation speed.

Natural gas has become an attractive alternative for diesel fuel due to its higher octane number, richer reserves and lower price. It has been utilized in compression ignition engines to obtain a higher thermal efficiency compared with spark ignition engines. However, its relatively higher auto-ignition temperature increases the difficulty of compression-ignition based on present hardware devices. One optimal ignition method is that a very small quantity of diesel fuel as the only ignition resource pilot-ignites the lean natural gas-air mixture. This micro diesel pilot-ignited natural gas premixed charge compression ignition (DPING-PCCI) combustion strategy is easy to implement without major hardware modifications, and can significantly reduce the NOx and particle mass emissions from diesel engines. Although the DPING-PCCI has so many advantages, it suffers from poor engine stability and high ultrafine particles emissions at part loads.

NASA is extending human exploration of space beyond the low earth orbit and moon to Mars. To save cost, it has been determined that In Situ Propellant Production (ISPP) is a key enabling technology in Mission to Mars. A cryocooler is needed to liquefy and store oxygen and methane on the Mars surface. In an earlier study by the authors, a single-stage reverse Brayton cycle cryocooler was proposed with neon as the working fluid. The cryocooler operates between 80K and 310K. It was shown that a highly effective recuperative heat exchanger is vital to the overall efficiency of the cryogenic system. To achieve a COP of 0.2 or better, the heat exchanger should have an effectiveness of 0.97 or better while the percentage pressure drop should be less than 3%. In this paper, the design and analysis of a highly effective micro heat exchanger is presented. The heat exchanger is a multi-layer pile of parallel square ducts. The cold and hot fluids flow in a counter flow manner.

A single-cylinder Gasoline Direct Injection Engine (GDI) engine with a centrally mounted spray-guided injection system (150 bar fuel pressure) has been operated with stoichiometric and rich mixtures. The base fuel was 65% iso-octane and 35% toluene; hydrogen was aspirated into a plenum in the induction system, and its equivalence ratios were set to 0, 0.02, 0.05 and 0.1. Ignition timing sweeps were conducted for each operating point. Combustion was speeded up by adding hydrogen as expected. In consequence the MBT ignition advance was reduced, as were cycle-by-cycle variations in combustion. Adding hydrogen led to the expected reduction in IMEP as the engine was operated at a fixed manifold absolute pressure (MAP). An engine model has also been set up using WAVE. Particulate Matter (PM) emissions were measured with a Cambustion DMS500 particle sizer.