This study was concerned with improvement and validation of a thermodynamic spark ignition engine simulation code developed in Leeds. Experimental validation data were generated using a central ignition, disc-shaped combustion chamber variant of a ported single-cylinder research engine with full-bore overhead optical access. These data included simultaneous measurement of cylinder pressure and flame position at different operating conditions. The engine was skip fired (fired once every five cycles), to remove residuals and ensure well defined in-cylinder fuel-air mixture for simulation. Flames were imaged using a digital camera capturing the light emitted from the flame ("natural light"). New methods were developed to process the pressure and film data. Flame pictures were processed to determine enflamed area, mean flame radius and flame centroid. Parameters were also developed to describe flame "circularity" ("shape factor") and to describe asymmetry of flame approach to the cylinder walls ("active perimeter fraction", APF). Time-base crank angle records allowed evaluation of engine speed variation within a cycle and mean engine speed for a cycle. Although generated principally for model validation, the experimental results proved interesting in their own right. Middle, slow and fast cycles were defined for each condition. Analysis of these cycles suggested that there was no correlation between the initial flame centroid displacement, its locus over the flame propagation period or the flame "shape factor" and the speed of combustion and pressure development. As the flame approached the wall, the active perimeter fraction fell in a similar manner for all the middle cycles. Substantial modifications were made to a pre-existing thermodynamic engine cycle code. Deficiencies in the blowby, heat transfer and thermodynamic aspects were corrected. An additional ("Zimont") turbulent burning velocity sub-model and a new routine for the influence of engine speed variation within a cycle were incorporated into the code. The active perimeter fraction parameter function determined in the experiments was encoded to allow for the effects of flame-wall contact on entrainment rate during the late flame propagation. A radial stratified charge model was also developed. Burned gas expansion over the flame propagation period was shown to significantly change the unburned gas charge stratification from the initial variation. Two types of initial stratification (linear and parabolic distributions, rich of the centre and lean close to the wall) were imposed. Faster combustion development was observed in both cases, c. f that for equivalent homogeneous charge. Good agreement was observed between experimental results and "Zimont model" predictions at different equivalence ratios and engine speeds. Other computations using the pre-existing Leeds K and KLe correlations gave reasonable predictions at the various engine speeds and at rich conditions; however, they yielded slower results than experimentally observed for lean conditions.

No description available.

Biogas as a fuel is attractive from a greenhouse standpoint, since biogas is carbon neutral. To be used as such, increasingly stringent emission standards must be met. Current low-emission technologies meet said standards by precisely controlling the air-fuel ratio. Biogas composition can vary substantially, making air-fuel ratio control difficult. This research was conducted as part of a larger project to develop a sensor that accurately measures biogas composition. Biogas was simulated by fuel mixtures consisting of natural gas and CO2; the effects that fuel composition has on emissions and catalyst performance were investigated. Engine-out THC and NOx increased and decreased, respectively, with increasing CO2 in the fuel mixture. Doubling the catalyst residence time doubled the conversion of THC and CO emissions. The effectiveness of the catalyst at converting THC emissions was found to be dependent on the relative proportions of engine-out THC, NOx and CO emissions.

Biogas as a fuel is attractive from a greenhouse standpoint, since biogas is carbon neutral. To be used as such, increasingly stringent emission standards must be met. Current low-emission technologies meet said standards by precisely controlling the air-fuel ratio. Biogas composition can vary substantially, making air-fuel ratio control difficult. This research was conducted as part of a larger project to develop a sensor that accurately measures biogas composition. Biogas was simulated by fuel mixtures consisting of natural gas and CO2; the effects that fuel composition has on emissions and catalyst performance were investigated. Engine-out THC and NOx increased and decreased, respectively, with increasing CO2 in the fuel mixture. Doubling the catalyst residence time doubled the conversion of THC and CO emissions. The effectiveness of the catalyst at converting THC emissions was found to be dependent on the relative proportions of engine-out THC, NOx and CO emissions.

The performance characteristics of a diesel fuel piloted syngas compression ignition engine are presented in this thesis. A stock Hatz 1D81 engine was converted to operate in dual fuel mode through the elimination of the governor system and addition of an in-cylinder pressure transducer and custom intake system to facilitate the mixing of the gaseous fuel and combustion air. The engine was run on a Superflow water brake dynamometer and benchmarked with diesel to compare against manufacturer specifications. This was followed by dual fuel operation on methane and syngas, with the results being compared through performance characteristics. When operated on methane, the engine attained higher peak in-cylinder pressures along with higher torque, power, and thermal efficiency values for equal equivalence ratios. It was necessary to use greater amounts of syngas to reach comparable results with methane due to the lower energy content of syngas. The ignition delay was greater for syngas, and the onset of knock occurred earlier with syngas in comparison to methane. The heat release, Q, was comparable for both fuels and the exhaust gas emissions were significantly lower for operation with syngas. With emphasis on clean engine operation, syngas operation proved to be viable due to its renewable nature, significantly lower exhaust gas emissions, equal heat release characteristics, and larger useable operating range when compared to methane. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2012-05-28 15:02:49.227

Controlling ignition timing and flame stabilization is one of the most outstanding challenges limiting the development of modern, efficient and low-emission compression ignition engines (CIEs). In this study, the role of turbulence on two-stage ignition dynamics and subsequent flame stabilization at diesel engine conditions is assessed by performing direct numerical simulations in a simplified inflow-outflow premixed configuration. The thermochemical conditions are chosen to match those of the most reactive mixture in the Engine Combustion Network’s n-dodecane Spray A flame (temperature of 813 K, pressure of 60 atm, equivalence ratio of 1.3, and with 15% vol. O2 in the ambient gas). Inflow velocities 4 to 16 times larger than the laminar flame speed are considered. As a result, in the absence of turbulence, ignition and flame stabilization are controlled by advection and chemistry, diffusion being negligible. Ignition delays match those of the homogeneous reactor and both the cool flame, due to low-temperature chemistry (LTC), and the hot flame, due to high-temperature chemistry (HTC), are spontaneous ignition fronts. Turbulence alters this picture in two ways. First, the second-stage (HTC) ignition delay is increased considerably, in contrast with the first-stage (LTC) ignition delay, which remains virtually unaffected. Second, a sufficiently high turbulence intensity makes the cool spontaneous ignition front transition to a cool deflagration which moves upstream to the inlet, while the hot flame is pushed downstream, still stabilized by spontaneous ignition. The latter phenomenon is caused by the reduced reactivity of LTC products as the cool flame transitions from spontaneous ignition to deflagration. Further increasing the turbulence intensity leads to both cool and hot flames transitioning to deflagrations. For the hot flame, the mechanism governing this transition is the increase in magnitude of progress variable gradient under increased turbulence or reduced inflow velocity, while in cool flames it is mainly due to the reduction in chemical source terms. In addition to turbulence intensity, the role of inflow velocity, integral length scale, and oxygen concentration level on this transition is assessed and modeling challenges are discussed. Finally, a chemical explosive mode analysis is provided to further characterise the ignition and transition phenomena. The present results highlight important fundamental roles of turbulence expected to modulate CIE combustion dynamics.

A 12.9 L heavy duty compression ignition engine was tested with strategies for dual fuel optimization. The effects of varied intake manifold pressure as well as split-injection strategies at a load of 5 bar BMEP and 85 PES were observed. These results were used to allow testing of split-injection strategies at a higher load of 10 bar BMEP at 70 PES that were void of MPRR above 2000 kPa/CAD. The split-injection strategies at 5 bar BMEP showed that lower BSNOx can be achieved with minimal drop in FCE. Varying intake manifold pressure revealed that combustion occurs earlier in a cycle with increasing intake manifold pressure and indirectly increasing FCE. A load of 10 bar BMEP at 70 PES should only use split-injection strategy to maintain load without high MPRR as efficiency drops with dependency on the second injection.

No description available.

On-board hydrogen and syngas production is considered as a transition solution from fossil fuel to hydrogen powered vehicles until problems associated with hydrogen infrastructure, distribution and storage are resolved. A hydrogen- or syngas-rich stream, which substitutes part of the main hydrocarbon fuel, can be produced by supplying diesel fuel in a fuel-reforming reactor, integrated within the exhaust pipe of a diesel engine. The primary aim of this project was to investigate the effects of intake air enrichment with product gas on the performance, combustion and emissions of a diesel engine. The novelty of this study was the utilisation of the dilution effect of the reformate, combined with replacement of part of the hydrocarbon fuel in the engine cylinder by either hydrogen or syngas. The experiments were performed using a fully instrumented, prototype 2.0 litre Ford HSDI diesel engine. The engine was tested in four different operating conditions, representative for light- and medium-duty diesel engines. The product gas was simulated by bottled gases, the composition of which resembled that of typical diesel reformer product gas. In each operating condition, the percentage of the bottled gases and the start of diesel injection were varied in order to find the optimum operating points. The results showed that when the intake air was enriched with hydrogen, smoke and CO emissions decreased at the expense of NOx. Supply of nitrogen-rich combustion air into the engine resulted in a reduction in NOx emissions; nevertheless, this technique had a detrimental effect on smoke and CO emissions. Under low-speed low-load operation, enrichment of the intake air with a mixture of hydrogen and nitrogen led to simultaneous reductions in NOx, smoke and CO emissions. Introduction of a mixture of syngas and nitrogen into the engine resulted in simultaneous reductions in NOx and smoke emissions over a wide range of the engine operating window. Admission of bottled gases into the engine had a negative impact on brake thermal efficiency. Although there are many papers in the literature dealing with the effects of intake air enrichment with separate hydrogen, syngas and nitrogen, no studies were found examining how a mixture composed of hydrogen and nitrogen or syngas and nitrogen would affect a diesel engine. Apart from making a significant contribution to existing knowledge, it is 3 believed that this research work will benefit the development of an engine-reformer system since the product gas is mainly composed of either a mixture of hydrogen and nitrogen or a mixture of syngas and nitrogen.

Student Number : 9707408V - MSc(Eng) research report - School of Mechanical, Industrial and Aeronautical Engineering - Faculty of Engineering and the Built Environment / This research is an investigation into the performance and combustion characteristics of a two-cylinder, four-stroke compression ignition engine fuelled on diesel and then on dimethyl ether (DME). Baseline tests were performed using diesel. The tests were then repeated for dimethyl ether fuelling. All DME tests were performed at an injection opening pressure of 210 bar, as recommended for diesel fuelling. The tests were all carried out at constant torque with incremental increases in speed and an improved method of measuring the DME flow rate was devised. It was found that the engine’s performance characteristics were very similar, regardless of whether the engine was fuelled on diesel or DME. Brake power, indicated power and cylinder pressure, during the highest loading condition of 55 Nm, were virtually identical for diesel and DME fuelling, with the most significant finding being that the engine was more efficient when fuelled on DME than when fuelled with diesel. Another interesting finding was that the energy release of diesel decreases with increasing load, whilst the energy release of DME increases with increasing load. At the highest loading condition of 55 Nm, the energy release of DME was approximately 210 joules higher than that of diesel. This investigation concluded that DME may definitely be a suitable substitute fuel for diesel.