Bengt W. Johansson

Effects of Different Type of Gasoline Fuels on Heavy Duty Partially Premixed Combustion

The effects of fuel properties on the performance and emissions of an engine running in partially premixed combustion mode were investigated using nine test fuels developed in the gasoline boiling point range. The fuels covered a broad range of ignition quality and fuel chemistry.The fuels were characterized by performing a load sweep between 1 and 12 bar gross IMEP at 1000 and 1300 rpm. A heavy duty single cylinder engine from Scania was used for the experiments; the piston was not modified thus resulting in the standard compression ratio of 18:1.In order to properly run gasoline type of fuels in partially premixed combustion mode, an advanced combustion concept was developed. The concept involved using a lot of EGR, very high boost and an advanced injection strategy previously developed by the authors.By applying this concept all the fuels showed gross indicated efficiencies higher than 50% with a peak of 57% at 8 bar IMEP. NOx were mostly below 0.40 g/kWh only in few operative points 0.50 g/kWh was reached. At high load the soot levels were mostly a function of the octane number; with RON higher than 95 it was possible to be below 0.5 FSN while for the more reactive fuels a peak value of 3 FSN was reached at 13 bar IMEP.The pressure rise rate reached a peak of 19 bar/CAD with fuels which had a RON above 95, when the octane number decreased below 90 the pressure rise rate was always below 14 bar/CAD. (Less)

Circadian distribution of onset of acute myocardial infarction in subgroups from analysis of 10,791 patients treated in a single center.

A circadian variation of symptom onset in acute myocardial infarction (AMI) with an increased frequency in the late morning and possibly also in the evening has been found in several studies. It has been suggested that different circadian rhythms may exist in various subgroups of patients. This possibility was examined in a population of 10,791 patients collected between 1973 and 1987 in a continuously operating register of patients with AMI in Malmö, Sweden. In 6,763 patients (63%) in whom a distinct symptom onset could be established, symptom onset occurred with an increased frequency between 6:01 A.M. and 12:00 noon (30.6%) and between 6:01 P.M. and 12:00 midnight (26.9%). Similar bimodal circadian rhythms were seen in patients aged greater than 70 years (n = 2,923), less than or equal to 70 years (n = 3,840), men (n = 4,528), women (n = 2,235), smokers (n = 2,458), hypertensives (n = 1,999), diabetics (n = 653), patients with (n = 1,872) and without (n = 4,891) a history of previous AMI, and in patients with recent non-Q-wave AMI (n = 333). In 455 patients receiving cardioselective beta blockers the circadian distribution did not differ from a random, whereas in patients taking nonselective beta blockers or calcium antagonists significant bimodal rhythms were found. Statistically significant interactions were found between symptom onset and age dichotomized at 70 years, and between patients with and without a history of previous AMI. In a multivariate analysis only these variables age less than or equal to/greater than 70 years; +/- history of a previous AMI) were found to modify the circadian rhythm of symptom onset in the population.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of low temperature on contraction in papillary muscles from rabbit, rat, and hedgehog.

During hibernation the body temperature may fall to only a few degrees above 0 degree C. The heart of the hedgehog continues to function whereas the hearts of nonhibernating mammals stop beating. The present study was performed to investigate and compare the mechanical responses to hypothermia in rabbits, rats, and hedgehogs. Isometric force was recorded from papillary muscles mounted in an organ bath and effects of hypothermia on the mechanical restitution curve were also compared. A reduction of bath temperature from 35 degrees C caused an increase in peak developed force. Maximum force was seen at 20 degrees C in the rabbit, 15 degrees C in the rat, and 10 degrees C in the hedgehog preparations. In all the species there was a similar prolongation of time to peak force and of time from peak to half-relaxation as temperature was lowered. An increase in resting force and after-contractions were recorded in the rabbit and rat muscles at temperatures below 15 and 10 degrees C, respectively. The rabbit and rat preparations became inexcitable at temperatures below 10 and 5 degrees C, respectively. The hedgehog papillary muscle, on the other hand, still contracted at 0 degree C and did not show increased resting force nor after-contractions. The results are consistent with the hypothesis that there is a calcium overload in cardiac cells from rabbit and rat at low temperatures but there is no calcium overload in the hedgehog muscle during hypothermia.

Temperature effects on the Na and Ca currents in rat and hedgehog ventricular muscle

Cardiac transmembrane potentials and Na and Ca currents were recorded at different temperatures in rat and hedgehog ventricular muscle. At 35 degrees C in both species resting potential was about -80 mV and upstroke velocity (Vmax) of the action potential above 100 V/s. The shape of the action potential in hedgehog ventricular cells at 35 degrees C was similar to that in the rat showing a fast repolarization phase. When temperature was decreased, the membrane resting potential depolarized and action potential amplitude and Vmax declined. In rat ventricular cells at 10 degrees C, the resting potential was about -40 to -50 mV and Vmax was reduced to about 5 V/s. In hedgehog ventricular cells, however, the transmembrane potentials and Vmax were better maintained at low temperature. Phase 3 of the action potential was markedly prolonged below 20 degrees C in hedgehog but not in rat ventricular cells. When temperature was decreased to 10 degrees C the availability curve of the Na current shifted toward more negative potentials and ICa.peak declined in rat ventricular cells. In hedgehog cardiac preparations, the Na current was less influenced by the cooling and ICa.peak did not change very much at low temperatures. A transient inward current usually considered to induce cardiac arrhythmias could be recorded in rat ventricular cells below 20 degrees C but not in hedgehog preparations. These features of hedgehog cardiac membranes may contribute to the cold tolerance and the resistance to ventricular fibrillation during the hypothermia in mammalian hibernators.

Ventricular fibrillation in hibernators and nonhibernators

Previous studies have shown that there are differences between hibernators and nonhibernators in the susceptibility to ventricular fibrillation. In an attempt to clarify these differences ventricular fibrillation was induced in isolated hearts of the hibernator, the woodchuck, Marmota monax by cooling, warming, puncture, and by norepinephrine administration. It was shown that the hearts of the winter animals were completely resistant toward the ventricular fibrillation inducing agents, which was not the case for the hearts from summer, active animals. Further, the hearts of another hibernator, the hedgehog, Erinaceus europaeus, and guinea pig, Cavia porcellus, were studied electrophysiologically in anesthetized animals with open chests and with bipolar electrodes attached to the epicardium. During pacing it was shown that the hedgehog had a higher stimulus threshold and a lower maximal following frequency than the guinea pig. The summer hedgehogs showed resistance toward both ventricular premature beats and ventricular fibrillation. Sixty percent of the summer hedgehogs and 100 percent of the winter hedgehogs and guinea pigs developed ventricular fibrillation. The threshold for ventricular fibrillation was highest for summer hedgehogs. The effective refractory period of papillary muscle of summer hedgehogs was shorter than that of guinea pigs. The force frequency relationship of the isolated papillary muscle showed a greater degree of independence in the hedgehog than in the guinea pig. Consequently, the results show that the heart of the hibernator is more arrhythmia resistant than the heart of the nonhibernator, although there are seasonal differences.

Combustion Stratification with Partially Premixed Combustion, PPC, using NVO and Split Injection in a LD - Diesel Engine

Partially Premixed Combustion (PPC) is used to meet the increasing demands of emission legislation and to improve fuel efficiency. PPC with gasoline fuels have the advantage of a longer premixed duration of fuel/air mixture which prevents soot formation at higher loads. The objective of this paper is to investigate the degree of stratification for low load (towards idle) engine conditions using different injection strategies and negative valve overlap (NVO). The question is, how homogenous or stratified is the partially premixed combustion (PPC) for a given setting of NVO and fuel injection strategy. In this work PRF 55 has been used as PPC fuel. The experimental engine is a light duty (LD) diesel engine that has been modified to single cylinder operation to provide optical access into the combustion chamber, equipped with a fully variable valve train system. Hot residual gases were trapped by using NVO to dilute the cylinder mixture. Optical measurements were carried out for OH chemiluminescence imaging to track sequentially the combustion process and to analyse the degree of stratification. Initial results show that the combustion with triple injection is more homogenous compared to single and double injection. Furthermore the results show that the 55 octane number fuel can be operated at low load condition with the lowest NVO used, 60 CAD. (Less)

The Clinical Outcome of Acute Myocardial Infarction Is Related to the Circadian Rhythm of Myocardial, lnfarction Onset

In order to study whether the circadian rhythm of acute myocardial infarc tion (AMI) onset has any impact on the clinical outcome, in terms of enzymati cally estimated infarct size, circulatory arrest from ventricular tachyarrhyth mias, and in-hospital mortality, the authors studied a representative population of 10,791 AMIs treated in the same center between 1973 and 1987. In 6,763 cases (63%) the time of symptom onset was known. In these cases a major peak in AMI incidence was observed between 7:01 AM and 10:00 AM, and minor peaks at 12:01 noon, 3:01 PM-4:00 PM, and 8:01 PM-9:00 PM. In a set of multiva riate analyses including several clinical characteristics, symptom onset between 6:00 AM and 12:00 noon significantly predicted a greater infarct size, and symp tom onset between 12:00 AM and 6:00, AM was associated with a significantly lower risk of circulatory arrests from ventricular tachyarrhythmias. The time of symptom onset was not significantly associated with in-hospital mortality after adjustment for other clinical characteristics, including infarct size. The authors suggest that the time of day has an impact, not only on the incidence, but also on the severity of AMI and that the ability of beta blockers to blunt the morning increase in AMI incidence may possibly contribute to the beneficial secondary preventive effects of such drugs after AMI.

The Effect of Intake Temperature in a Turbocharged Multi Cylinder Engine operating in HCCI mode

The operating range in HCCI mode is limited by the excessive pressure rise rate and therefore high combustion induced noise. The HCCI range can be extended with turbocharging which enables increased dilution of the charge and thus a reduction of combustion noise. When the engine is turbocharged the intake charge will have a high temperature at increased boost pressure and can then be regulated in a cooling circuit. Limitations and benefits are examed at 2250 rpm and 400 kPa indicated mean effective pressure. It is shown that combustion stability, combustion noise and engine efficiency have to be balanced since they have optimums at different intake temperatures and combustion timings. The span for combustion timings with high combustion stability is narrower at some intake temperatures and the usage of external EGR can improve the combustion stability. It is found that the standard deviation of combustion timing is a useful tool for evaluating cycle to cycle variations. One of the benefits with HCCI is the low pumping losses, but when load and boost pressure is increased there is an increase in pumping losses when using negative valve overlap. The pumping losses can then be circumvented to some extent with a low intake temperature or EGR, leading to more beneficial valve timings at high load.

Effect of beta blockade on ventricular fibrillation-and ventricular tachycardia-induced circulatory arrest in acute myocardial infarction☆

The risk of developing circulatory arrest secondary to ventricular fibrillation or tachycardia in acute myocardial infarction (AMI) is greatly increased in patients with hypokalemia, whether diuretic induced or not. In a retrospective study of 5,877 infarctions during an 8-year period, hypokalemia was more common (22.5%) in diuretic-treated AMI patients than in those not treated with diuretics (12.9%). Thus, hypokalemia should be avoided in diuretic-treated patients with increased risk of myocardial infarction. Circulatory arrest occurred in 13% of hypokalemic patients treated with nonselective beta blockers on admission compared with 26% in those treated with selective beta blockers. No difference was found in normokalemic patients. The mean serum potassium value was 4.07 mM/liter in the patients treated with nonselective beta blockers compared with 4.0 and 4.01 in those treated with selective and no beta blockade, respectively. In a separate study, adrenaline infusion in healthy volunteers produced a decrease not only in serum potassium but also in serum magnesium, although the latter occurred later. Pretreatment with verapamil exaggerated the decrease in serum potassium. When starting beta-blocker treatment in patients at risk of developing AMI, consideration should be given to commencing with a nonselective instead of a selective beta blocker.

Metabolic, Hemodynamic, and Electrocardiographic Responses to Increased Circulating Adrenaline: Effects of Pretreatment with Class 1 Antiarrhythmics:

In order to study the effects of treatment with class 1 antiarrhythmics on the metabolic, hemodynamic, and electrocardiographic responses to adrenaline, 12 healthy volunteers were infused on four occasions, after pretreatment with placebo, disopyramide, mexiletine, and flecainide, respectively, with adrenaline at a rate producing serum adrenaline concentrations comparable with those seen in acute myocardial infarction. After pretreatment with placebo adrenaline caused significant falls in serum potassium, serum magnesium, serum calcium, and se rum phosphate and a significant increase in blood glucose. Adrenaline also caused a significant increase in heart rate and systolic blood pressure and a significant fall in diastolic blood pressure. On the electrocardiogram a significant prolon gation of QTc duration and a flattening of the T-wave amplitude were seen. Pretreatment with disopyramide had no effect on the hemodynamic response to adrenaline but caused a significant prolongation of Qtc duration before the adrenaline infusion. Pretreatment with mexiletine was associated with a signifi cantly greater fall in serum potassium during adrenaline infusion, and pretreat ment with flecainide with a greater fall in serum magnesium, as compared with placebo pretreatment Flecainide also caused a significant prolongation of the QRS duration before adrenalin infusion, and after all the active pretreatments a prolongation of QRS duration was seen during adrenaline infusion. The meta bolic and hemodynamic changes during adrenaline infusion may not only reduce the antiarrhythmic efficacy of antiarrhythmics but may also increase the risk of proarrhythmic effects in a clinical setting. These results may help to explain why treatment with antiarrhythmics seems to be without beneficial effect on mor tality in post-myocardial infarction patients.