EP0105509A2 - Low pressure diesel engine - Google Patents

Abstract

A low pressure diesel engine is proposed in which the combustion pressures do not substantially exceed those of spark ignition engines and the combustion temperatures are far below those of the spark ignition process so that the engine power can be raised when using existing models of this design. The basis of the proposal is formed by the combination of a diesel motor with a charging device, preferably with a rotational pivot charger according to the European Patent 0,012,329, the advantages of this latter device being retained: greatly reduced fuel consumption particularly in the partial load region, engine characteristic made closer to the ideal traction force hyperbola, low working speed, reduced noise, less toxic exhaust gases. For this purpose the compression ratio of the diesel engine is lowered to approximately the range of the spark ignition engines which is still favourable thermodynamically so that ignition of the injected fuel would not take place and the necessary ignition temperature would be ensured by heating up the charging air by the corresponding amount. This heating up occurs in the motor working ranges in which the compression heat of the charger is not sufficient, preferably by means of a flame and its hot combustion gases in the charging air current. Variants, for example the use of electrical energy in any form, are possible. Very light-weight two-stroke low pressure diesel engines are thus easy to construct with low specific consumption, favourable characteristic and low weight and are particularly suitable for driving small aeroplanes. <IMAGE>

Description

The invention relates to an internal combustion engine which works according to the diesel method and which has a charging device using the exhaust gas energy, preferably a rotary vibrating charger according to the European patent O o12 329 as a free-moving charging unit, but especially with a 2-stroke diesel engine also with a driving connection to Engine, charge air under pressure at least in certain working areas of the engine and in which the compression ratio is reduced so far that even taking into account the heat of compression of the charge air during the compression stroke of the engine, the temperature required for igniting the injected fuel at least in unfavorable ambient conditions when starting and at partial load, is not reached.

Apart from known ignition aids, a compression end temperature of 500 ° is required for the diesel engine to safely ignite the injected fuel. According to the gas laws, this requires a high compression ratio and a correspondingly high pressure for the normal naturally aspirated engine.

In car engines, which have to start safely at a pass height and with considerable degrees of cold, compression ratios are around 23: 1, which results in a compression end pressure of around 70 bar.

Because of the better thermodynamic efficiency, the constant pressure process originally envisaged by Diesel has been largely modified so that combustion pressures above 100 bar are more likely to be regarded as normal. These engines are then subjected to even higher peak pressures when they are charged by exhaust gas turbochargers or Comprex pressure wave machines, whereby 170 bar can also be reached or even exceeded.

So that these motors withstand the high loads, they have to be built much heavier than gasoline engines. The higher weight means a significantly higher price, so that the diesel engine, which is cheaper in terms of fuel consumption than car drives, is only reluctantly gaining acceptance on the market. The rule applies that only those who drive more than 150,000 km / a can achieve relative cost savings.

To remedy this unsatisfactory state of development by reducing the peak pressures, particularly in vehicle diesel engines, to values comparable to those of the Otto process, without impairing the characteristic favorable properties of the diesel process, is the purpose of the present invention.

High engine weights are particularly unpleasant for aircraft. For a long time, strong forces have been set in this area to solve the problem of combining low-cost fuel consumption with a low engine weight.

The state of development in this regard can be characterized by NASA's attempts to build 2-stroke low-pressure diesel engines for smaller aircraft. This process, called low compression diesel, is described in the US _A journal "Popular Science", issue April 1982, page 1 ₀₃ and the like. The basis for this is apparently a further developed hyperbar process, the basic features of which can be seen in K. Zinner: Supercharging of internal combustion engines - 2nd edition - 1980 - Springer-Verlag Berlin, in Section 9.7.

The process as it was developed by Teledine on behalf of NASA is shown schematically in Fig.1.

At the start of the internal combustion engine 1, the unit consisting of the compressor 2 and the turbine 3 is driven by the powerful electric motor 4. By the switched valve 5 is supplied at 6 angesangte air above the combustion chamber 7 of the turbine 3 and this begins, the L _a de ggregat _a driving 2-3. If the speed is high enough, the charge air is heated by compression to approx. 3.7 bar by approx. 123 ⁰ .

After switching the valve 5, the engine 1 can now be supplied with heated charge air and its exhaust gases then drive the turbine 3 - even when the combustion chamber 7 is switched off

The compression ratio of the engine is reduced so far that the ignition temperature for the injected fuel is reached at a charge air temperature of 123 ⁰ . The bar is at a boost pressure of 3.7 compression end pressures of about 55 bar, and so in the said source is a ^V erbrennungsenddruck 1 ₀ 4 bar as "low" means that compared to the similarly specified 140 bar for marketable diesel engines well applies.

Incidentally, a charge air cooler, which is not shown in FIG. 1 and is designed as an air-air unit, is provided so that the charge air quantity is not reduced in operation by the charge air temperatures being too high. This is certainly necessary because it is a turbocompressor, the pump limit of which, as is well known, limits the ratio of delivery volume and delivery head.

In addition, the efficiency, particularly in the case of smaller turbomachine units, is so low that the combustion chamber has to constantly supply energy, especially in the part-load range.

For car engines, which are not only interesting for industry due to their large number of items, but also require special attention due to their environmental impact, this system cannot be used for physical reasons due to its low performance, but also cannot be used due to the effort involved.

In contrast, according to the proposed invention, favorable results should also be achieved with these mass engines. Not only by simple design and clear equipment, but also by optimal behavior in the partial load range - the main field of work of car engines - by a characteristic favorable for vehicles and low consumption values with low pollution polluting exhaust gas.

To solve this problem, the invention provides that, with a reduced compression ratio of the diesel engine, the charge air combined by the pre-compression in the supercharger and by heating is heated to such an extent that the ignition temperature at the end of the compression stroke of the engine is reached at a substantially reduced pressure, so that at a suitable one Law of injection the maximum combustion pressure remains in the order of magnitude that occurs in gasoline engines.

This charge air is preferably heated losslessly by a combustion process in the charge air flow, but it is also another heat source, e.g. Implementation of electrical energy applicable.

It should be noted that this is a combination of special charging from the start and heating of the charge air, especially in certain engine work areas, while heating of the intake air is not unknown as a starting aid for normal diesel engines.

A normal heating register with heat exchange to the charge air, without direct mixing of the heating gases and charge air, is not so cheap because of the efficiency of this transfer and is also more expensive in terms of material. However, later, when the engine is running, the engine exhaust gases still flowing out of the drive unit of the loading assembly at a considerable temperature could be used for heating. This would perhaps be of interest in the partial load range and above all in the 2-stroke engines, which are much more demanding due to the need for purge air.

You could also add hot engine exhaust to the charge air to heat it. This measure could be carried out without effort when using a rotary vibratory loader in which both gases flow side by side.

A practical _m is the application of the operating substance of the diesel engine for heating. However, given the low proportion of the heating energy, which will generally be less than 5%, it is also possible to use a more easily igniting medium, for example a liquid gas, for the addition of hot water use tongue.

The charge air heating is probably not ignited by a constantly burning pilot flame, but controlled electrically according to the proven state of the art, e.g. through spark gap or film arc. This also makes it easy to combine a check whether the heating is in operation and its regulated throttling until it is switched off in certain working areas of the engine.

In a vehicle drive, the preferred field of application of the invention, this ignition and control device is expediently coupled to the starting process of the engine.

It is particularly emphasized that this invention is outstandingly suitable for use in 2-stroke diesel engines, taking into account the regulations applicable to the rotary vibratory loader to be used, since at the same time the required purge air is available.

• Der Ottomotor ist leicht und drehfreudig, also insofern günstig für den Antrieb von Fahrzeugen. Leider ist er wegen des nur in gewissen Grenzen des Luftverhältnisses zündfähigen Arbeitsgemisches dem Dieselmotor in bezug auf den spezifischen Brennstoffverbrauch grundsätzlich unterlegen, wie dies in Fig.2 ersichtlich ist. Außerdem wird sein PV-Diagramm bei Teillast thermodynamisch schlechter, da dabei günstige Diagrammteile abgeschnitten werden. Beim Dieselmotor ist es gerade umgekehrt. Bei ihm entfallen dabei ungünstige Diagrammteile, sodaß er sich bei Teillast thermodynamisch verbessert.

The advantages of the invention are diverse and easy to demonstrate:

• The petrol engine is light and easy to turn, so it is cheap for driving vehicles. Unfortunately, because of the working mixture that is ignitable only within certain limits of the air ratio, it is fundamentally inferior to the diesel engine in terms of specific fuel consumption, as can be seen in FIG. 2. In addition, his PV diagram gets worse thermodynamically at part load, since cheap diagram parts are cut off. The reverse is true for diesel engines. He does away with unfavorable diagram parts, so that he improves thermodynamically at part load.

Because the air ratio can only be changed within narrow limits, the exhaust gas temperature of the gasoline engine is always high, so that a lot of energy flows out. In contrast, the air ratio of the diesel engine at part load is particularly high, w _a s shown in Fig. 2 results in a favorable fuel consumption and low exhaust gas temperatures.

In city traffic, a medium-sized car needs to be on a level SSE a drive power of about 5 kW, which at a 1.5 - 2 liter engine with ooo min ^-1 bar is derived an average effective pressure of approx. 2 These 2 bar to coat already significant that a gasoline engine needs to run strongly throttled in this area and accordingly a negative average pressure of ca - drags _0, 75 bar.

The turbocharged supercharged engine according to the diesel process - if you call it a low-pressure diesel engine with a rotary vibratory supercharger - on the other hand experiences an additional boost even at partial load when changing loads due to the difference in boost pressure and the engine exhaust gas flowing to the supercharger of maybe + 0.5 bar - above calculated throughout the entire working cycle.

Compared to the 2 bar of the mean effective pressure of the required net power, -o, 57 and + o, 5 bar are very significant amounts, which determine the fuel consumption in city traffic.

Lower fuel consumption per se means less toxic exhaust gas, in which the NO _x components are also low because of the much lower temperatures of the engine working cycle with a high air ratio in the proposed low-pressure diesel engine + rotary rocker loader.

• Überlegenen spezifischen Brennstoffverbrauch - besonders in dem für PKW-Antriebe so wichtigen Teillastbereich; hohe Drehmomente auch bei geringen Motordrehzahlen, günstige Luftverhältnisse im ganzen Motorarbeitsbereich. Durch dem Motor angepaßte Drehzahl des Rotationsschwingladers ist seine direkte Ankopplung beim Startvorgang des Motors möglich, sodaß ohne zusätzliche Apparatur sofort geheizte Ladeluft zur Verfügung steht, aber auch die Spülluft für einen 2-Takt-Dieselmotor.

The invention makes the proposed low-pressure diesel engine as light as a gasoline engine, but retains the advantages of the diesel process in connection with those of the rotary vibratory loader:

• Superior specific fuel consumption - especially in the partial load range that is so important for car drives; high torques even at low engine speeds, favorable air conditions in the entire engine working range. The speed of the rotary vibratory charger, which is adapted to the engine, enables it to be coupled directly when the engine is started, so that heated charge air is immediately available without additional equipment, but also the purge air for a 2-stroke diesel engine.

It should be mentioned that practically every model of gasoline engine changes the cylinder cover for this low-pressure diesel process could be used: the pressures remain within comparable limits and the temperatures become lower. This, in turn, enables a significant increase in performance without much effort from the model. The valves could be made smaller in order to accommodate a swirl chamber in the cylinder cover, for example, since the rotary vibratory loader compensates for flow losses.

With the rotary vibratory loader, there is no mutual dependency between the flow rate and the delivery head, and there is no restriction like the surge limit of turbochargers. It does not bother him much when charging the engine with heated charge air, since the reduction in charge air mass can be compensated for by increasing the charge pressure.

If one arranges the heating between the supercharger and the engine, the heating does useful work due to the expansion of the charge air. Therefore, this arrangement is cheaper than that before entering the compressor, because then the charger has to cope with a larger volume.

The prior art provides means to optimally adapt the heating to the respective needs, the working area of the engine and the ambient conditions. So you will e.g. Heat up higher when starting and later turn back the heating when the engine is warmed up and lay it out in such a way that it can be omitted in the main work areas. This is a question of coordinating the overall unit, and it is also important that the heating by direct flame and its fire gases is not very expensive.

• Bei einem Luftverhältnis von 2 wird für 1 kg Brennstoff im Motor ca 28,6 kg Luft benötigt. Um diese Luftmenge um 1₀₀° zu erhitzen, sind 72o kcal erforderlich, also ca 72 g Dieselöl, welche ihrerseits zur Verbrennung 1 kg Luft benötigen, also 3,5% der Arbeitsmenge, so daß das Luftverhältnis sich auf 1,93 ändert - was zu vernachlässigen wäre!

It is easy to prove that this direct heating of the charge air by hot fire gases does not cause a significant disturbance in the air ratio or significant energy losses:

• At an air ratio of 2, about 28.6 kg of air is required for 1 kg of fuel in the engine. In order to heat this amount of air by 1 ₀₀ °, 72o kcal are required, i.e. about 72 g of diesel oil, which in turn is 1 kg for combustion Need air, that is 3.5% of the amount of work, so that the air ratio changes to 1.93 - which would be negligible!

The additional warming must be taken into account in the swallowing line diagram of the motor Fig. 3. Therein, 7 are the swallowing lines of the engine at different speeds, 8 are the respective purge air fractions, 9 are the throughputs, taking into account a heating of the charge air that drops from p _l = 1 bar. 1o is the loading line at full load, 11 that at partial load, 12 the loader curve at its maximum speed. The ones underneath run in parallel with the speed.

Since you will hardly go under an engine compression ratio of 7: 1 to maintain a favorable thermodynamic efficiency, a charge air compression of 2.5 bar can be expected without exceeding the maximum combustion pressures in a gasoline engine, provided you have a corresponding injection law for to be loaded _- nen low-pressure diesel engine used. However, this charge pressure already results in a sufficiently high charge air temperature under favorable ambient conditions, so that additional heating can be dispensed with even in the partial load range. This means that the engine intake lines do not change in the decisive range compared to the usual values. -The visible reduction in the throughput volume due to the heating but is irrelevant in the start-up area and during the lower part-load operation, since there is anyway a significant air ratio.

So far, mainly the properties that make the combination of low-pressure diesel engine + charge air heating + rotary swing loader an optimal engine, especially for cars, have been discussed. This special status is a partly achieved by connecting the respective advantageous properties of gasoline and diesel engines, the other part but to allow by the ability of Rotationsschwing- l _{A is} the charge from the start and idle to drive any high boost pressures, without GR _s entliche losses the engine conditions in GESAM adapt the work area, bring high air conditions and thus cheap exhaust gas and, in contrast to all other supercharging processes, also ensure favorable fuel consumption values even at partial load. Also important is the property of optimally supplying the engine from idle to full load without noticeable delay and without precarious operating conditions, such as exceeding the smoke limit.

But precisely these advantages are not given and it means a severe handicap if instead of charging the low-pressure diesel engine with a rotary oscillating charger, the charge air heater is used with one of the known charging devices, e.g. Combined exhaust gas turbocharger or pressure wave machine Comprex.

In fact, when using the charge air heater, even with any normal exhaust gas turbocharger and also without additional electromotive drive of the charging unit, a low-compression diesel engine, which must start as a naturally aspirated engine in the exhaust gas turbocharger and Comprex, can be started and driven.

At a compression ratio of, for example 9: 1 heating of the charge air by about 100 ° is sufficient in order to achieve with certainty ^o i-ignition temperature of the injected fuel. This means that one could have every passenger car diesel engine provided with exhaust gas turbocharging optimally compressed, thereby eliminating the previous problem that the normal naturally aspirated engine is exposed to combustion pressures that are much too high with all their unpleasant consequences.

• Bei Heizung vor dem Verdichter wird das Ansaugvolumen vergrößert, also die Durchsatzmenge des Motors reduziert, was seine Schlucklinien im Arbeitsfeld des Verdichters verschiebt. Es entstehen aber keine Schwierigkeiten durch die lυmpgrenze des Verdichters.

However, it should be noted that such an application in cars or other land vehicles, the operation of which requires the traction force hyperbole, does not lead to optimal results comparable to the use of a rotary vibratory loader, since only this machine, which works on the displacement principle, harmoniously adapts to the piston engine. On the other hand, when using an exhaust gas turbocharger, the following adjustment difficulties arise, depending on whether the charge air is heated up before or after the turbo compressor. or after the turbocompressor:

• When heating upstream of the compressor, the intake volume is increased, i.e. the throughput of the engine is reduced, which shifts its intake lines in the working area of the compressor. However, there are no difficulties due to the compressor's high limit.

In contrast, in the case of heating after the turbocompressor, the motor would react to the conveyance of air in accordance with the ambient conditions with a retrospective increase in the boost pressure, which easily leads to the pump limit being exceeded.

In any case, the air filling of the engine cylinders is reduced and special measures must be taken to ensure that the smoke limit is not exceeded during the transition from idling to the work area. The acceleration for land vehicles will be reduced. By contrast, the procedure for ships and aircraft would be applicable because their propeller curve rises slowly in the power so that an exhaust gas turbocharger has time to adapt to the conditions of ^V ollastbetriebes his behavior.

Fig. 4 shows the embodiment for a low pressure diesel engine with an exhaust gas turbocharger and a charge air heater according to the invention. The engine starts without significant delay if the flame 15 is ignited in good time when the starter is actuated.

4, 1 is the low-pressure diesel engine to be charged, 13-14 the exhaust gas turbocharger with the exhaust gas turbine 13 and the turbocompressor 14, 15 the heating flame with the automatic ignition and regulating device 16, which receives its control impulses from the control device 17. 18 is the adjustable fuel pump for the flame 15.

The actual invention proposal is described in somewhat more detail with reference to FIG. 5 as a summary of the general description to date with the use of a rotary vibratory loader: The rotary vibratory loader 19 in FIG. 5 supplies it in its compression ver ratio suitably adapted internal combustion engine according to the diesel method 1 with charge air. This is heated by the Fl _a m-me 15 by direct heat transfer and by mixing with its fire gases. An ignition and control equipment 16 after ^b tand art controls this process, wherein the heating intensity is approximately regulated according to the needs safe ignition and unnecessarily high temperature by control of the heat-sensing 17th The flame 15 is fed by the fuel pump 18. 2o is the temporary possible driving connection between the engine and the rotary vibratory loader during the starting process. This connection is essential for 2-stroke engines and state of the art Rotationsschwingl _a.

Instead of the flame 15, e.g. an electrical resistance heater or a flame arc can be arranged.

It is also possible to heat the charge air by means of a heating register, not shown, which must be externally heated at the start, while the register should be heated by engine exhaust gases after the engine has started.

A direct admixture of hot engine exhaust gases - after a differently initiated engine start - to the charge air is understandable without a graphic representation according to the state of Teehnik.

The advantages of the low-pressure diesel engine according to the invention in the optimal combination with a rotary vibratory loader are particularly impressive when viewed in connection with the use of such a device for driving a highly motorized vehicle, e.g. of a car, considered.

The gearbox required between the vehicle and the engine can then be designed as a Föttinger converter, which could also be followed by a so-called mountain gear. However, it could also be self-reinforcing according to the state of the art in converter technology, as in a Rieseler transmission, and even integrate reverse gear by reversing the function of the impeller and idler.

The gear pumps available for the circulation of the converter operating medium can also be used for wear-free braking.

The conditions are optimal if this Föttinger transmission contains a Trilok converter, the coupling point of which corresponds as closely as possible to the maximum engine torque.

Claims (9)

Internal combustion engine according to the diesel process to which a charging device with utilization of the exhaust energy, preferably a rotary oscillating loaders according to the European Patent o o12 329 ggregat as a free-traveling charging _a, however, especially in a 2-stroke diesel engine with drivingly connected to the engine, charge air under pressure at least in certain working areas of the engine and in which the compression ratio is so low that even taking into account the heat of compression of the charge air during the compression stroke of the engine, the temperature necessary for igniting the injected fuel does not reach at least in unfavorable environmental conditions, when starting and under partial load is characterized in that the charge air is additionally heated in the critical areas by a heat source in the charge air flow before entering the working cylinders of the engine. Device according to claim 1, characterized in that the heat source is a low-loss heater with direct mixing of the charge air with fire gases from a combustion process. Device according to claim 1, characterized in that the charge air is heated by a heat source fed by electricity, a flame arc or a glow device. , Device according to claims 1 to 3, characterized in that a control member designed according to the prior art is provided, which monitors and controls the ignition and effectiveness of the heating device. Device according to claims 1, 2 and 4, characterized in that for heating the charge air instead of the normally used engine fuel, a more flammable medium, e.g. a liquefied petroleum gas is used. Device according to claims 1 to 5, characterized in that the triggering of the charge air heating is coupled with the starting process of the engine, an advance and a safety device being provided if the heating fails. Device according to claim 1, preferably as a low-pressure 2-stroke diesel engine, characterized in that at the start and in the areas in which the energy of the engine exhaust gases, even with additional heating, is not sufficient for the effective operation of the rotary vibratory loader, a driving connection between the rotary vibratory loader and There is an engine, which can be switched off automatically as soon as the loader becomes free. Device according to one of claims 1 to 7, which is used as a drive in a highly motorized vehicle, preferably in a car, characterized in that it is connected as a transmission between the engine and the vehicle with a hydrodynamic converter, with or without a mountain gear, the Trilok-type converter and is designed so that its coupling point corresponds approximately to the highest engine torque. Device according to claim 8, characterized in that the hydrodynamic torque converter alone represents the complete vehicle transmission, in which the reverse gear is also integrated by reversing the function of impellers and idlers, while the gear pumps available for the circulation of the converter operating medium are simultaneously used as wear-free brakes can.

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