Soot processes in compression ignition engines

Power production from biomass derived pyrolysis liquids has been under development for the past few years. If technically successful, it would make decentralized bio-energy production possible. Several technologies and system components have been developed by academia, R&D organizations, and industrial companies in many countries. Much experience has been gained and many useful results published. The present work aims at reviewing the most significant experience in power generation from biomass liquids produced by fast pyrolysis processes. Power plant technologies addressed are diesel engines, gas turbines, and natural gas/steam power plants. Main results are reviewed and R&D needs identified for each technology. The analysis shows that even for the most promising solutions long-term demonstration has not yet been achieved. Pyrolysis liquid use in gas turbine plants and in co-firing mode in large power stations are technically most advanced. Recent work with diesel engines also appears quite promising.

http://www.combio-project.com/download/PDF/Power_generation_using_fast_pyrolysis_liquids_from_biomass.pdf

Power generation using fast pyrolysis liquids from biomass

Effects of soybean biodiesel on a DI diesel engine performance, emission and combustion characteristics

Performance and combustion characteristics of a di diesel engine fueled with waste palm oil and canola oil methyl esters

Engine experiments have shown that with highpressure multiple injections (two or more injection pulses per power cycle), the soot-NOx trade-off curves of a diesel engine can be shifted closer to the origin than those with the conventional single-pulse injections, reducing both soot and NOx emissions significantly. In order to understand the mechanism of emissions reduction, multidimensional computations were carried out for a heavy-duty diesel engine with multiple injections. Different injection schemes were considered, and the predicted cylinder pressure, heat release rate and soot and NOx emissions were compared with measured data. Excellent agreements between predictions and measurements were achieved after improvements in the models were made. The improvements include using a RNG k-e turbulence model, adopting a new wall heat transfer model and introducing the nozzle discharge coefficient to account for the contraction of fuel jet at the nozzle exit. The present computations confirm that split injection allows significant soot reduction with out a NOx penalty. Based on the computations, it is found that multiple injections have a similar NOx reduction mechanism as single injections with retarded injection timings. Regarding soot reduction, it is shown that reduced soot formation is due to the fact that the soot producing rich regions at the spray tip are not replenished when the injection is terminated and then restarted. With split injections, the subsequently injected fuel burns rapidly and does not contribute significantly to soot production. The present work also demonstrates the usefulness of multidimensional modeling of diesel combustion to reveal combustion mechanisms and to provide design insights for low emission engines. EXTENSIVE RESEARCH is in progress to reduce both nitrogen oxides (NOx) and particulate (soot) emissions from diesel engines due to environmental concerns. One of the emission-control strategies is in-cylinder reduction of pollutant production. It is well known that it is very difficult to reduce both NOx and soot production simultaneously during the combustion process. Many emission-reduction technologies developed so far tend to increase soot emission while reducing NOx emission, and vice versa. For example, retarding fuel injection timing can be effective to reduce NO formation. However, this usually results in an increase of soot production. On the other hand, although increasing fuel injection pressure can decrease soot emissions, it can also cause higher NOx emissions at the same time [1]*. Recently, it has been shown experimentally that with high-pressure multiple injections, the soot-NOx trade-off curves of a diesel engine can be shifted closer to the origin than those with single-pulse injections, reducing both soot and NOx emissions significantly [2-4]. Nehmer and Reitz experimentally investigated the effect of double-pulse split injection on soot and NOx emissions using a single-cylinder Caterpillar heavy-duty diesel engine [2]. They varied the amount of fuel injected in the first injection pulse from 10 percent to 75 percent of the total amount of fuel and found that split injection affected the sootNOx trade-off. In general, their split-injection schemes reduced NOx with only a minimal increase in soot emissions and did not extend the combustion duration. Tow et al. [3] continued the study of Nehmer and Reitz [2] using the same engine, and included different dwells between injection pulses and triple injection schemes in their investigation. They found that at high engine load (75%), particulate could be reduced by a factor of three with no increase in NOx and only a 2.5% increase in BSFC compared to a single injection, using a double injection with a relatively long dwell between injections. They also found that triple injection could reduce NOx and soot emissions at both light and high loads. Another important conclusion of Tow et al. [3] is that the dwell between injection pulses is very important to control soot production and there exits an optimum dwell at a particular engine operating condition. The optimum dwell of a double-injection was found to be about 10 degree crank angles at 75% load and 1600 rev/min for their engine conditions. * Numbers in brackets designate References at the end of the paper. Pierpont et al. [4] confirmed that the amount of fuel injected in the first pulse affects the particulate (smoke) level in experiments where the NOx emission level was held constant. However, the best double injections were found to also depend on the spray nozzle included angle. For a production injector with a 125 included angle, which results in significant wall impingement on the piston bowl, the best double injections were found to be those with 50% to 60% of the fuel injected in the first pulse. They also found that with a combination of EGR and multiple injections, particulate and NOx were simultaneously reduced to as low as 0.07 and 2.2 g/bhp-hr, respectively, at 75% load and 1600 rev/min. Other multiple injection studies can be also found in the open literature [5, 6]. The published experimental works indicate that multiple-injection is an effective mean to control NO and particulate production during the diesel combustion process. In general, multiple injections allow the injection timing to be retarded to reduce NOx emission while holding the particulate at low levels. Both the amount of fuel injected in the first pulse and the dwell between pulses are important for an optimum injection scheme. With the application of multiple injection technology, the goal of improved injection scheme design and better control of engine combustion is made difficult by the fact that design variables are added with flexible injectors. It is thus helpful to simulate the engine processes with the use of computational models, which can provide detailed temporal and spatial information of precisely parameter-controlled injection and combustion processes. Patterson et al. [7] performed multidimensional computations of multiple injections using an improved KIVA code. They tried to reproduce the experimental results of Nehmer and Reitz [2] and achieved a fair success. However, the accuracy of their model prediction deteriorated for double-pulse injections as the amount of fuel injected in the second pulse increased. Kong, Han and Reitz [8] modified the code by including a modified RNG k-e turbulence model and turbulence boundary conditions [9]. Predictions of combustion and emissions of single-injections were shown to be improved significantly [8]. These successes motivated the application of the code to multiple injections in the present study. It is clear that a good model is necessary in order to predict engine combustion and emissions accurately. Accordingly, the submodels used by Kong, Han and Reitz [8] were implemented together with improved heat transfer and injection models. The models were first applied to the experimental results of the double injections of Nehmer and Reitz [2]. For better understanding of the formation of NO and soot during multiple-injection combustion processes, a set of designed singleand double-injection schemes were computed. Based on the computational results, a mechanism of emission reduction using multiple-injection is suggested.

Mechanism of Soot and NOx Emission Reduction Using Multiple-injection in a Diesel Engine

Diesel Combustion Improvements by the Use of Oxygenated Synthetic Fuels

Running Light-Duty DI Diesel Engines with Wood Pyrolysis Oil

Some oxygenated hydrocarbons were tested as pure fuels in two different DI diesel engines, and their emission potential was compared to n-tetradecane combustion. Two colours pyrometry method was used to infer in-cylinder sooting tendency of tested fuels. Pure pyrolysis of the same fuels was also investigated in a conventional shock lube at high temperature (1700–2500 K) and pressure (9–13 bar), using light scattering/extinction methods. All oxygenated compounds tested in the engines exhibited a strong decrease of soot loading compared with tetradecane combustion. The long soot induction times, as measured in shock tube experiments, and the oxygen content of the fuel molecules seem to provide a plausible explanation of soot lacking in oxygenated fuels combustion. Emission measurements at the exhaust of a four cylinder engine fully confirm the trends obtained by two colours pyrometry and shock tube experiments. As a matter of fact, the oxygenated synthetic fuels strongly reduce both gaseous and total partic...

Experimental Characterization of Combustion Behaviour of New Diesel Fuels for Low Emission Engines

Potentiality of Oxygenated Synthetic Fuel and Reformulated Fuel on Emissions from a Modern DI Diesel Engine

Using a modified version of the Kiva-2 code, three-dimensional computations of combustion and soot formation were performed, burning tetradecane and n-heptane in a direct injection, naturally aspirated diesel engine A coupled soot formation and combustion model is proposed Assuming acetylene as the crucial pyrolitic species, the model takes into acount the fuel-to-acetylene pyrolysis, acetylene oxidation, soot nucleation, and surface growth and soot oxidation The numerical predictions are compared with the expermental data of heat-release patterns and with the in-cylinder measurements of acetylene concentration and soot volume fraction C2H2 data were collected using a fast-acting valve, while soot loading was measured with the two-color technique The improved code is able to predict correctly the combustion and heat-release patterns of the two fuels without any retuning of the model constants The computational results demonstrate that the reduced kinetic soot model is capable of predicting, with satisfactory accuracy, the local amount of soot and pyrolytic products in the combustion chamber, keeping the main features of the diesel combustion

N. Del Giacomo

Papers

Diesel Combustion Improvements by the Use of Oxygenated Synthetic Fuels

Running Light-Duty DI Diesel Engines with Wood Pyrolysis Oil

Experimental Characterization of Combustion Behaviour of New Diesel Fuels for Low Emission Engines

Potentiality of Oxygenated Synthetic Fuel and Reformulated Fuel on Emissions from a Modern DI Diesel Engine

Application of a reduced kinetic model for soot formation and burnout in three-dimensional diesel combustion computations