DE2936127A1 - Compression ignition IC engine - has fuel heated in absence of air above ignition point before injection into cylinders - Google Patents

Abstract

The engine is constructed as a diesel engine with direct fuel injection. One or more heat exchangers are inserted between the injection pumps and the cylinders. The fuel is heated in these when it is at pressure to a temp. above its ignition temp. When it is injected into the cylinders it ignites as soon as it meets the oxygen in the air in the cylinders. Combustion and expansion then follow immediately. When the engine is warm the necessary heat is drawn from the exhaust gases. When the engine is cold or lightly loaded an auxiliary electric source of heat is used.

Description

Description of the invention

An alternative combustion process with improved efficiency for reciprocating and rotary piston engines O. Introduction The escalating situation in the energy sector, in particular the looming oil shortage and price increase, makes it appear more and more urgent to deal with the possibilities of a better one To deal with energy utilization. in the following, on the basis of a theoretical consideration It will be shown which measures can currently be used to reduce consumption on car engines.

Advance consideration To deal with an efficiency improvement in internal combustion engines To be able to deal, it is necessary to look at the current state of the art visualize in order to then use the identified weaknesses of the respective Combustion process (Otto or Diesel process) starting points for an efficiency to find improvement.

1. The Otto engine The mixture formation and combustion process of the Otto engine should be well known. The efficiency of the combustion process is calculated here as follows: 1? th (Seiliger) where: Vh + Vc # = = V1 / V2 = compression ratio Vc # = P3 / P2 = T3 / T2 = pressure increase ratio # = V4 / V3 = T4 / T3 = injection ratio # = Cp / Cv = isentropic exponent in approximation to the actual ratios a mixture of equal space and equal pressure processes is defined. (Seiliger process, see also Fig. 1 + 2) The calculation of the efficiency according to the equation overleaf assumes that the specific heat capacity is constant. However, this is not the case. For precise calculations, T, S or H, S diagrams should therefore be used for combustion gas, in which the change in the specific heat capacity and the influence of dissociation at high temperatures are taken into account.

The Seiliger efficiency is not quite achieved in the engine. A measure for the approximation the quality grade is: indexed efficiency #g = # i / # th = Seiliger efficiency The existing deterioration is caused by: -Unprogram- and - discharge - incomplete combustion - throttle losses - leakage losses na at Otto engine practically under controls the combustion at V = const. takes place, can however, by a simple equal space comparison process (FIG. 3) a relative one achieve an exact approximation of the actual conditions. The efficiency simplifies in this case to: b.w.

#th = 1 - T1 / T2 = 1 - (1 / #) @ - 1 If you wear #th depending on the Compression ratio # on (Fig. 4), the known fact can be read off, that the thermal efficiency is better with increasing compression.

The overall efficiency (#ges = # th. # G. # M), however, is somewhat different Characteristic. The cause is the mechanical efficiency with increasing compression falls due to the higher friction losses (Fig.5), so that ultimately for the Overall efficiency of a motor with compression of £ = 12 # 16 (depending on the motor) sets a maximum value (Fig. 6).

The compression ratio in the gasoline engine may be due to the otherwise occurring, Knocking 'do not exceed the value of 9.5 i 10.5, so that the maximum value of t ges ges is not reached.

Partial load operation is much worse, in which due to the quantitative mixture control (throttle losses!) the effective compression ratio is further reduced.

A partial or complete cylinder deactivation could be a remedy which some automobile plants have been working on for some time. In the partial load range the remaining cylinders with higher load (# higher effective compression # better efficiency). The wall to be driven and the gain in efficiency vary in size, depending on whether: - a mixture switch-off (20% better) + -a mixture and gas exchange switch-off (30% better) + -a complete cylinder switch-off (40% better) + (division of the crankshaft) + is selected based on the ECE City Test.

Another alternative would be a rotor with variable compression, in which the compression is increased in partial load operation. On such a test engine currently works at Daimler Benz.

At present, these internal combustion engines are sizeable because of the Additional costs are not yet profitable.

Summary: The main disadvantages of the gasoline engine are: - # # always well below the ideal compression ratio because of the risk of knocking.

-due to the quantitative mixture control, additional efficiency losses in partial load operation.

2. The diesel engine Comments on the combustion process For everyone so far executed diesel engines, the intake air must be pre-compressed to the extent that that the ignition temperature for the injected fuel is clearly exceeded During the injection process, the fuel is over the edge of the injection lobe warmed up The evaporated fuel then finally begins to heat up in the hot air to ignite and thus initiates combustion.

Because at the beginning of the injection the surface of the fuel lobe and the temperature difference between air and fuel is limited, passes thus a long time until the combustion speed of the injection speed is equivalent to. This period of time is called "ignition delay" (order of magnitude approx. 2 ms).

During the ignition delay, more fuel is injected than burned. This excess amount is then burned abruptly, which is a results in a large pressure gradient dp, which in turn results in a high engine load and noise (knocking or nailing) is present.

On the other hand, it follows that the tapping or nailing behavior of a The shorter the ignition delay, the better the diesel engine will be.

The different types of diesel engines When the diesel engine is to distinguish between the plane-chamber motors (antechamber and vortex chamber) and the Direct injection engines (DE, usual DE and DE based on the M process).

In terms of efficiency, the direct injection engines have a clear advantage, like the one from Daimler-Benz on a 2.2 ltr. Diesel engine in which the cylinder head has been modified on a case-by-case basis figure 7).

The reasons for this are: - More favorable surface-volume ratios with direct injection, therefore less': heat losses during and after combustion.

- No hydraulic shift losses (with pre-chamber engines are these are larger than with vortex Kanerriotors, therefore vortex chambers have an advantage here.) -Ways better surface-to-volume ratio, less heat loss during compression # Operation with lower compression (# = 12 + 18) possible.

Note: It should also be used with direct injection for use in cars because of the small cylinder units and the resulting relatively poor surface-to-volume ratio (Area proportional to the square of the outer dimensions - volume proportional to the third power of the dimensions) a slightly higher compression can be selected.

The direct injection has compared to the sub-chamber engines at the moment but there are still serious disadvantages, so that the direct injection engine is to be used for the time being does not seem likely in a car: To keep the ignition delay small, you need the diesel engine creates a strong, turbulent air movement in the combustion chamber. This mui9 die tear open the injected fuel lobe, which increases the surface area, which in turn results in better heat transfer and thus a smaller ignition delay Consequence.

In the case of sub-chamber engines, there is a strong movement of air during the Compression stroke generated when the sucked air through the shot channels into the Secondary chambers flows. In addition, there is a greater compression due to the greater compression Gas temperature and thus also a greater temperature difference #T (Q # #T) available.

In the case of direct injection, the necessary air movement must already be achieved during of the intake stroke (e.g. by a swirl channel) This has the following Disadvantages: a) No such strong air movement as with sub-chamber motors A worse Tear open the injected Fuel lobe # greater ignition delay # higher engine load and higher combustion noise # larger engine masses # lower maximum speed.

b) There are difficulties, the swirl requirements over a to meet larger speed range. The ratio should be half of the nominal speed <4 idle speed cannot be exceeded. (A swirl channel allowed due to its high throttle resistance at high gas speeds none anyway high speeds).

c) From a) and b) it follows that the limited speed increases the power density is smaller in the direct injection engine than in the auxiliary chamber diesel engine. Could remedy Here, however, for example, can be created by an exhaust gas turbocharger.

3. Summary and objectives for a consumption-optimized combustion process As can be seen from the foregoing, are to create a consumption-optimized Combustion process, the following conditions must be met: - £ # 12 + 16 (2 total maximum) - qualitative mixture control (otherwise reduction of the effective compression = Loss of efficiency in partial load operation) This shows that d at today's level the technology of the direct injection diesel engine is also the most economical for use in passenger cars Solution would be if it succeeds in its design disadvantages compared to the alternative diesel engines or the gasoline engine. The disadvantages of the direct injection diesel engine, however, practically all of them rely on the greater ignition delay traced back. There could also be a strong swirl generation during the intake stroke be waived if the ignition delay is reduced in another way or completely switched off could be. A measure to reduce or prevent the ignition delay is described in the following chapter.

4. Proposal of a modified combustion process As on the As described on the last pages, only the ignition delay prevents use of the direct injection diesel engine in the car. This in turn is caused by the gas side Heat supply (what is meant here is the heat that initiates combustion).

If you would now instead of the air, the fuel before: injecting over beyond the ignition point (for the pressure and temperature conditions in the combustion chamber) heat, there should be practically no ignition delay, because the fuel immediately after passing the injector due to the pressure drop that occurs (see below) would evaporate and burn immediately due to the high internal temperature. One, Preparation of the fuel in the combustion chamber would therefore no longer be necessary. Through this the compression could then be optimized in terms of efficiency. aside from that The air movement in the clean room would only have to be so great that there is enough oxygen is approached to the injected fuel. This shouldn't be particularly problematic like the former Daimler-Benz engine of the 300th SL proved that had direct injection (lso into the combustion chamber).

For the heating of the fuel one could of course use the waste heat from the engine, especially the exhaust heat.

This would result in another advantage: while with conventional ones Diesel engines during the injection process needed to prepare the fuel Thermal energy of the compressed air and thus the subsequent expansion stroke is withdrawn, this energy is available practically free of charge in the proposed case Disposal. (Use of the exhaust gas heat!) Exact figures about the warming and evaporation enthalpy are currently in the required pressure and temperature range for diesel fuel not yet published anywhere.

Based on experience and comparisons with other fuels or liquid hydrocarbon compounds one can make a very rough estimate. Accordingly, the energy required should be between 300 - 1000 kJ / kg. One goes assume that when one kg of diesel oil is burned, approx. 10,000 kJ of thermal energy become free, there is an additional energy gain of approx. 3 - 10%.

When using such a motor, the battery capacity (compared to today's diesel engines), because by the lower Compression would require the starter less power. In addition, the cold start preheating take place within a largely thermally insulated component. (At today's Diesel engines not possible because the combustion chamber must not be thermally insulated.) In the figures 8 and 9 show the conditions for a diesel engine with "fuel-side heat supply" qualitative (not possible in quantitative terms, as precise figures for diesel fuel not available, see above) shown in a p, T diagram and a T, S diagram.

In Figure 8 it can be seen that the fuel (theoretically all liquid fuels could be burned in such an engine) at the time of the start of injection is beyond the "critical point" in the state diagram. That means, despite the high preheating temperatures, the fuel does not evaporate until the Pressure drop during the injection process in the combustion chamber.

In FIG. 9, the heating process after the injection has taken place is for shows the fuel in a modern diesel engine (dashed line from 1) after 2)).

The area under the curve shows the energy required for this. It was roughly assumed that this process takes place isobarically.

The dash-dotted line gives the isobaric p = (= "critical pressure") again.

The solid line from 3) to 4) represents the heating process for an appropriately modified engine.

which takes place here at a higher pressure (p> pK).

The end point of the heating should be as far to the right in the T, S as that even after the pressure drop during injection and the associated Temperature decrease the ignition temperature is exceeded (see 5)). as one can easily see from the T, L, diagram that in this case for the heating of the fuel a larger amount of heat must be provided, which, however should not have a disadvantageous effect, since here the heat, as already mentioned, is practical free of charge (exhaust heat!).

Other restrictions are due to a "fuel-side heat supply" not given. For example, in this case too, charging by an exhaust gas turbocharger could be performed or Comprex loader.

5. Constructive execution Constructive would be with such a Engine doesn't change much from a traditional direct injection diesel engine. Only the fuel would have to be heated after passing through the injection pump through the exhaust manifold. Then the other line must up Ground the injector well with heat (e.g. by asbestos coating). It is advisable to attach the cold start heating device at this point, since this way the heat losses that occur can be kept small.

Of course, the system must be free of air, otherwise a premature combustion would stop because the ignition temperature is already during of the heating process in the pressure lines exceeded. (See also Fig.

8 + 9).

Increased demands are only made of the pressure lines, which must be resistant to both pressure and temperature. The injection pump could do the correspond to today's, because now only cold fuel must be promoted. (A notable heat return against the direction of flow is not likely!).

A buffer would have to be installed between the injection pump and the valve the pressure increase and / or volume expansion. of fuel during the heating process, which also varies depending on the operating state of the rotor can be, catches so that there is no unwanted 'injection. Farther this buffer would have to ensure that the pressure in the injection lines is not falls below the critical pressure "pK (also Fig. 8 + 9).

It could possibly be due to the existing elasticity of the injection lines the necessary "buffering effect" can be provided.

The injection valve should, if it is not positively controlled, a have strong hysteresis, i.e. there should be a clear difference between the There are opening and closing pressures. This could ensure that the pressure rise that occurs during the heating process does not lead to an undesired increase Injection leads. Such a valve is shown in a functional sketch in FIG reproduced.

Functional description (Fig. 10) If the piston is raised at high pressure, this increases the pressure application area, which, in addition to rapid opening of the Valve has the consequence that the valve is only at a much lower pressure closes again.

This means that when the valve is closed, the fuel is fed sufficiently quickly can flow back again, a circumferential groove is provided, which in turn goes through Bores is connected to the main fuel line.

The needle is lifted by a driving device with the piston nd by a spring if necessary with the closed Valve on his Seat pressed.

By choosing the appropriate spring and surface, every injector can and closing pressure and thus also every ratio of these pressures can be determined.

Another advantage of this injector would be that there is no post-injection occurs when the pressure wave generated by the injection pump is reflected.

6. Special problem Wankel engine The diesel concept was previously used in the Wankel engine very difficult to achieve. The reason for this are the structural conditions; because in order to achieve the required compression, (it has to be higher with a rotary engine than with a comparable reciprocating engine, because the compression process is there takes place over a larger surface and thus higher heat losses occur, especially since the compression only takes place in the "cold part" of the trochoid.) becomes higher K-factor generating trochoid radius required. #K - factor = #. With eccentricity However, the base circle of the eccentric shaft must have a high K factor because of the synchronizing teeth stay relatively small. The pitch circle diameter of the relevant gear ring is 4 X eccentricity, i.e. H. , the base circle must remain well below it. This results in difficulties in supporting the forces that occur.

So far, only Wankel diesels have been built, which either a precompaction took place through a complete second trochoid with a runner, or those with huge dimensions (such as that of Prof. G. Jungbluth test diesel engine developed for Magirus Deutz), in which As a general rule the power density is lower and thus the relative load is lower.

If one now applies the new principle here, one could use the smaller one Compression a Wankel diesel engine can be built to address these problems. Through this This may open up a completely new opportunity for the Wankel principle, because in that than the already known advantages of the Wankel engine (high power density, low Weight, compact design and smooth running) together with low consumption will occur.

Claims (1)

Claim # 1 modified, improved in efficiency. Combustion process for piston engines (especially reciprocating and rotary piston engines) with direct Kraftsteffeln Spritzang, with which it is possible to burn all liquid fuels, and thereby dis is characterized in that with a "fuel-side heat supply" the introduction The heat required for combustion is fed into the combustion chamber. This makes it possible most of the other engine parameters (e.g. compression, combustion chamber shape and intake duct design) largely free according to the respective required point of view (e.g. efficiency and exhaust gas). About the "fuel-side heat supply" in high-speed engines To be able to realize, the following procedure is suggested: -After passing A high pressure pump, usually the injection pump, is used to deliver the fuel in the High pressure line heated. The heat must be supplied under pressure to prevent evaporation of the fuel and thus a volume multiplication occurs. She must also be so large that after opening the injection valve solely through the contact of Fuel initiated the combustion with the oxygen in the combustion chamber will. -For heating up the fuel, it is advisable to use the Abga @@ @@@ hermzu, as this promises a further improvement in efficiency. - For the starting process (and possibly less operation tracks here Load where the exhaust gas heat alone is not sufficient - whether there are such operating points there at all, would first have to be clarified by appropriate measurements), is through external heating (e.g. electrical) to bridge the heat deficit. Note: Pei engines with large cylinder units (e.g. Marine diesel), which already have a theoretically ideal compression ratio are operated from 12 - 16, an external heating would not be necessary because there due to the favorable surface-volume ratios the "air-side heat supply" one safe combustion guaranteed. However, the achievable gain in efficiency would then also be here limited to the use of exhaust gas heat.