Alcohols, because of their potential to be produced from renewable sources and because of their high quality characteristics for spark-ignition (SI) engines, are considered quality fuels which can be ...blended with fossil-based gasoline for use in internal combustion engines. They enable the transformation of our energy basis in transportation to reduce dependence on fossil fuels as an energy source for vehicles. The research presented in this work is focused on applying
n-butanol as a blending agent additive to gasoline to reduce the fossil part in the fuel mixture and in this way to reduce life cycle CO
2 emissions. The impact on combustion processes in a spark-ignited internal combustion engine is also detailed. Blends of
n-butanol to gasoline with ratios of 0%, 20%, and 60% in addition to near
n-butanol have been studied in a single cylinder cooperative fuels research engine (CFR) SI engine with variable compression ratio manufactured by Waukesha Engine Company. The engine is modified to provide air control and port fuel injection. Engine control and monitoring was performed using a target-based rapid-prototyping system with electronic sensors and actuators installed on the engine
1. A real-time combustion analysis system was applied for data acquisition and online analysis of combustion quantities. Tests were performed under stoichiometric air-to-fuel ratios, fixed engine torque, and compression ratios of 8:1 and 10:1 with spark timing sweeps from 18° to 4° before top dead center (BTDC). On the basis of the experimental data, combustion characteristics for these fuels have been determined as follows: mass fraction burned (MFB) profile, rate of MFB, combustion duration and location of 50% MFB. Analysis of these data gives conclusions about combustion phasing for optimal spark timing for maximum break torque (MBT) and normalized rate for heat release. Additionally, susceptibility of 20% and 60% butanol–gasoline blends on combustion knock was investigated. Simultaneously, comparison between these fuels and pure gasoline in the above areas was investigated. Finally, on the basis of these conclusions, characteristic of these fuel blends as substitutes of gasoline for a series production engine were discussed.
•NG/diesel RCCI engine was simulated by Converge CFD model.•By increasing the PR, the lower reactivity of NG causes lower combustion rate.•Increasing first injected fuel quantity results in higher HC ...and CO emissions.•Narrower spray angles have higher values of HC and CO emissions.
Reactivity controlled compression ignition (RCCI) combustion mode is an attractive combustion strategy due to its potential in satisfying the strict emission standards. In this study, the effects of direct injection (DI) strategies on the combustion and emission characteristics of a modified light duty RCCI engine, fueled with natural gas (NG) and diesel were numerically investigated. In this way, Converge CFD code employing a detail chemical kinetics mechanism was used for 3D simulation of combustion process and emissions prediction. NG with higher octane number (ON) is mixed with air through intake port, while diesel fuel with lower ON is directly injected into the combustion chamber during compression stroke by means of split injection strategy. The effects of several parameters, including the premixed ratio (PR) of NG, diesel fuel fraction in first and second injection pulses, first and second start of injection timing (SOI1 and 2), injection pressure and the spray angle on the engine performance and emission characteristics are investigated. The results indicate that these parameters have significant effects on the light duty RCCI engine performance and engine out emissions. Also, it was demonstrated that by decreasing the first injection pressure from 450 to 300bar, the gross indicated efficiency increases by 5% and CA50 is retarded by 4 CAD. Moreover, by reducing the spray angle from 144° to 100°, the gross indicated efficiency decreases by 4% and CA50 is advanced by 6 CAD. The results showed that reduction in NOx emission is achievable, while controlling HC and CO emissions, by means of increasing the NG fraction, advancing the SOI1, increasing the fuel fraction in first DI injection with lower injection pressure and employing a wider injector spray angle.
•Exhaust residuals affect both combustion, engine performance and exhaust emissions.•Exhaust residuals strongly affect NOx, THC and CO.•Exhaust residuals do not change substantially fuel ...consumption.•Higher internal exhaust residuals cause longer combustion duration.
Exhaust gases remaining inside the engine cylinder after the exhaust stroke premix with fresh air-fuel combustible mixture and affect combustion process in the engine cylinder. Due to significantly higher temperature of these exhaust residuals (ExR) compared to the external exhaust gases recirculation (EGR), their impact on the in-cylinder combustion process is also different from impact of EGR. To control amounts of ExR independent of engine working parameters, the variable valve timing was introduced. It is known that variable valve timing affects not only volumetric efficiency and performance of the internal combustion reciprocating engine but also influences the amount of exhaust residuals remaining in the engine cylinder. These exhaust residuals impact combustion rates, combustion stability, knock and also play crucial role on exhaust toxic emissions. In this manuscript, the effect of variable valve overlap was studied on A. exhaust toxic emission (NOx, CO and THC), and B. combustion phasing and engine performance on a spark ignited natural gas fueled engine.
The investigation was carried out in a single cylinder research engine at constant load. The engine was equipped with high authority dual independent cam phasors for both intake and exhaust values, but for the purpose of this study, the exhaust valve timing was fixed and intake valve timing was changed to vary the amount of exhaust residuals remaining in the engine cylinder. The correlation between valve overlap and exhaust residuals were determined. It was observed that correlation in the positive overlap range between 55 and 85 deg was almost positive linear. Regarding toxic exhaust emission, increase in exhaust residuals from 9.6 to 12.3% (change by 28%) caused reduction in NOx by 67% and increase in both CO and THC by approximately 75%. Additionally, it did not significantly affect the engine’s specific fuel consumption. Summarizing, strong correlation between in-cylinder exhaust residuals and toxic emissions, and combustion phases exists in the methane fueled spark ignited engine equipped with VVT.
Whenever antipsychotic medication is not effective, the first intervention should be to check adherence. If the intake of the oral medication is “relatively” sure and no relevant side effect occurs, ...the dosage should be increased, if necessary to the maximal tolerated dosage. If side effects do not allow any further increase of the dosage and the antipsychotic drug is taken without any relevant improvement, switching to another antipsychotic is an option most often used. Several issues should be considered: Change only one drug at a time, switch to an antipsychotic with a different pharmacological profile, ask the patient for his/her collaboration, document psychopathology and tolerability before switching and plan to do again two to four weeks after switching to assess success of switching. The switching strategy has been investigated in several studies and no major difference has been found. However, cross tapering for a period of three to seven days is most often used and probably the safest procedure. The efficacy of switching the antipsychotic, although often used in daily practice, has not well been investigated yet. The few clinical studies will be presented. Data can be summarized: to switch from the first atypical antipsychotic to the second, is effective in 20 to 30%, the switching to a third atypical antipsychotic (if not clozapine) is very seldom successful. After two unsuccessful attempts a switch to clozapine should be thoroughly considered.
The article discusses the results of experimental studies on the course of pyrolysis oil injection through the high-pressure injector of a direct-injection engine. The pyrolysis oil used for the ...tests was derived from waste plastics (mainly high-density polyethylene—HDPE). This oil was then distilled. The article also describes the production technology of this pyrolysis oil on a laboratory scale. It presents the results of the chemical composition of the raw pyrolysis oil and the oil after the distillation process using GC-MS analysis. Fuel injection tests were carried out for the distilled pyrolysis oil and a 91 RON gasoline in order to perform a comparative analysis with the tested pyrolysis oil. In this case, the research was focused on the injected spray cloud analysis. The essential tested parameter was the Sauter Mean Diameter (SMD) of fuel droplets measured at the injection pressure of 400 bar. The analysis showed that the oil after distillation contained a significant proportion of light hydrocarbons similar to gasoline, and that the SMDs for distilled pyrolysis oil and gasoline were similar in the 7–9 µm range. In conclusion, it can be considered that distilled pyrolysis oil from HDPE can be used both as an additive for blending with gasoline in a spark-ignition engine or as a single fuel for a gasoline compression-ignition direct injection engine.
While operating at light loads, diesel pilot-ignited natural gas engines with lean premixed natural gas suffer from poor combustion efficiency and high methane emissions. This work investigates the ...limits of low-load operation for a micro-pilot diesel natural gas engine that uses a stoichiometric mixture to enable methane and nitrogen oxide emission control. By optimizing engine hardware, operating conditions, and injection strategies, this study focused on defining the lowest achievable load while maintaining a stoichiometric equivalence ratio and with acceptable combustion stability. A multi-cylinder diesel 6.7 L engine was converted to run natural gas premix with a maximum diesel micro-pilot contribution of 10%. With a base diesel compression ratio of 17.3:1, the intake manifold pressure limit was 80 kPa(absolute). At a reduced compression ratio of 15:1, this limit increased to 85 kPa, raising the minimum stable load. Retarding the combustion phasing, typically used in spark-ignition engines to achieve lower loads, was also tested but found to be limited by degraded diesel ignition at later timings. Reducing the pilot injection pressure improved combustion stability, as did increasing pilot quantity at the cost of lower substitution ratios. The lean operation further reduced load but increased NOx and hydrocarbon emissions. At loads below the practical dual-fuel limit, a transition to lean diesel operation will likely be required with corresponding implications for the aftertreatment system.
Dual nature of hydrogen combustion knock Szwaja, Stanislaw; Naber, Jeffrey D.
International journal of hydrogen energy,
09/2013, Letnik:
38, Številka:
28
Journal Article
Recenzirano
Combustion knock is abnormal combustion taking place in an internal combustion spark ignited engine. It might be particularly observed in the engine at the end of combustion when the air–fuel mixture ...residue can be self-ignited due to exceeding auto-ignition temperature of this mixture. However, while hydrogen is combusted the knock can also occur as a result of non-auto-ignited combustion events. Investigation on knock, presented in the manuscript, was conducted in a hydrogen fueled spark ignited single cylinder engine with variable compression ratio. To express in numbers intensity of the combustion knock the in-cylinder pressure pulsations were used as a credible metrics. On the basis of analysis of these pulsations the hydrogen knock was distinguished as light and heavy one depending on its origin. The light knock is generated by combustion instabilities, which are a source for generating pressure waves inside the engine cylinder. The heavy knock results from hydrogen auto-ignition at the end of combustion. Its intensity is several times higher in comparison to the light knock. These observations were additionally confirmed by analysis of heat release rate. Finally, the light and the heavy knock were characterized by average amplitude of the pulsations from the entire test series of hundreds and several thousands kPa, respectively.
•A hydrogen fueled spark ignited CFR engine was applied for investigation.•Study on hydrogen knock was conducted vs. variable engine compression ratio.•Light and heavy knock were recognized and examined.•Intensity of the light knock depends on temperature of hydrogen–air mixture.•Intensity of the heavy knock is associated with mass of hydrogen self-ignited.
Phasing and duration are two of the most important aspects of combustion in Spark Ignition (SI) engines. They impact efficiency, emissions, and overall engine performance. These aspects of combustion ...can be represented by the mass fraction burn (MFB) profile. Having an accurate mathematical model of the MFB profile leads to an ability to model the combustion process and, thus, properly model the overall engine in 1D engine simulation tools.
The Wiebe function is widely used in engine simulation to estimate the MFB profile as a function of crankshaft position. In this work, for the purpose of validating a sub-process, the Wiebe function parameters were calculated using an analytical solution and a least squares method by fitting MFB locations, as determined from analysis of measured cylinder pressure, to both single and double-Wiebe functions. To determine the accuracy of the respective Wiebe function, a single-zone pressure model was applied to reconstruct the pressure trace. Once the pressure trace is recovered, the reconstructed pressure trace is then compared with the experimentally measured cylinder pressure trace. Results showed that the double-Wiebe function model fit better than the single-Wiebe function model. The root mean square error (RMSE) of the reconstructed pressure trace using the double-Wiebe estimation is 7.9 kPa. In comparison, the RMSEs of the reconstructed pressure traces using the single-Wiebe analytical solution and single-Wiebe least squares methods were 70.0 kPa and 75.9 kPa, respectively, demonstrating a significant improvement.
► The Wiebe function is widely used in engine simulations to represent the mass fraction burn profile as a function of crankshaft position. ► In many cases, a single Wiebe function does not sufficiently represent the mass fraction burn profile, particularly under high dilution and knocking combustion conditions. ► A double-Wiebe function can be used to characterize the non-symmetric combustion resulting from extreme engine operating conditions. ► It is found that the double-Wiebe function model fit the experimental mass fraction burn profiles better than the single-Wiebe function model.
The benefit of neuroleptic drugs in the treatment of schizophrenic patients is objectively beyond any doubt. However, most patients discontinue their neuroleptic drugs within some months. This low ...compliance might be caused by the lack of insight into the disease and the necessity of therapy. Also of major importance are adverse effects, not restricted to motor symptoms, but also affecting cognition and emotion. They are often too subtle to be detected by objective examination, but reported by patients who complain of a reduced quality of life with restrictions of emotionality, straight thinking and spontaneity. This syndrome, similar to negative symptoms of schizophrenia, has been named 'pharmacogenic depression' or 'neuroleptic-induced deficit syndrome'. To investigate this issue of major clinical relevance, a self-rating scale was developed to measure subjective well-being under neuroleptic treatment (SWN). First analyses indicate good practicability, reliability, validity and sensitivity. Data obtained from 280 remitted schizophrenic patients showed that the SWN was significantly correlated to objective psychopathology (Positive and Negative Symptom Scale, PANSS; r = -0.35), quality of life (r = 0.60) and other self-ratings of mood states Profile of Mood Scale (POMS), Self-rating Depression Scale (SDS), Befindlichkeits Scale (BFS); r = 0.25-0.75. A repeated application after 3 months in 53 patients did not show any change in SWN in those with constant neuroleptic medication, but there were marked alterations if the dosage or the drug was changed. The SWN in 28 patients treated with clozapine because of therapy resistance or major side effects was, despite negative selection, significantly better (t = 1.79, p = 0.03) than in 38 patients under classical neuroleptics. Moreover, even at dismissal, patients who were non-compliant 4-6 months later (n = 14) differed significantly (t = 3.21, p = 0.02) in SWN, but not in PANSS, from those who remained compliant (n = 34). These data indicate that the SWN is a useful tool for investigating a hitherto neglected psychopathological dimension. Subjective effects of neuroleptics are measurable, affect patients' quality of life and should be considered more thoroughly in clinical routine as well as in clinical trials of potential neuroleptic drugs.