The following vehicles were used in the tests carried out for this report: -
A - SACHSENRING P240 - A new car produced from 1956 until 1959 in the nationalised Horch factory at Zwickau. It had a 6-cylinder overhead valve motor of 2407 cc (The Trabant is still made in this factory). https://dkwautounionproject.blogspot.com/2022/08/1956-sachsenring-p240-english-brochure.html
B – WARTBURG 311 - Three-cylinder two-stroke engine.
https://dkwautounionproject.blogspot.com/2021/01/1956-wartburg-311-brochure-english.html
C- VOLKSWAGEN - 1954 Beetle with a 1192 cc. horizontally opposed four-cylinder side-valve motor producing 30 h.p.
The twentieth century is marked by the rise of the motorcar. Now that modern, largely automated, mass production methods reign supreme, possession of a car is coming within the scope of ever greater parts of the population. This has led to a rapid growth of traffic density which in some countries is taking on alarming proportions, especially in towns. Simultaneously, service and garage facilities have not been able to keep pace. Thus, it is only natural that during recent years the general trend is increasingly towards smaller and cheaper cars requiring but little maintenance.
In this context, the question of the advantage the two-stroke engine has to offer is bound to arise.
The usual two-stroke engine has the advantage of operating without the outlay the timing gear that a four-stroke engine necessitates. Thus, such expensive parts as camshafts, camshaft drives, push rods, rockers and their bearing brackets, valve and guide assemblies are omitted. In addition, cylinder heads are much. simpler and can be produced at a material cost saving. Because mixture lubrication is employed with two-stroke engines, a circulatory lubrication system is unnecessary and lubricating oil pumps, filters and piping can be dispensed with. Among other things, this simplifies the manufacturing process of the engine crank case. In this connection the problem of filtration of lubricating oil cannot be overlooked because the modern four-stroke engine requires considerable outlay for this. In order to obtain high piston displacement power rating and still keep the wear within tolerable limits, not only high-quality oil must be used, but satisfactory filtering must be provided for with the aid of main and auxiliary filter equipment. Often special oil coolers are required because the lubricating oil is also utilized for cooling purposes in this type of engine. It is evident that the two-stroke engine can be manufactured at a material cost saving because this equipment is not required. With a water-cooled two-stroke engine for use under European climate conditions it is even possible to omit the water circulation pump. Due to the simple design of the two-stroke engine, and principally because of the simple cylinder head design, there are no places which will tend to overheat if the flow of cooling water is too slow, therefore the utilization of the thermo-syphon cooling system is quite feasible. However, this does not preclude the possibilities in comparison with a four-stroke engine of the same rating. Generally, a smaller piston displacement is needed by the two-stroke engine to attain a certain output respective to a certain torque value. This again results in lower outlay of raw material. Furthermore, the use of material of as high a quality as for the four-stroke engine is not necessary for the construction of a two-stroke engine. This finally leads to the other advantage of a two-stroke engine in that it is much lighter than its four-stroke equivalent.
Besides the advantages offered in manufacture and cost, additional advantages result in operation. The operating cost of a motor vehicle is made up of fixed and variable components. Regarding the fixed cost component of the two-stroke engine, there are advantages in such countries where motor vehicles are taxed according to the size of piston displacement because for a desired motor torque the two-stroke engine requires a smaller working volume than a comparable fourstroke engine. The variable cost component is also determined by the utilization of the vehicle, the yearly mileage being considered as the respective characteristic. This factor contains the cost of fuel, maintenance and repair. The opinion is often voiced that compared with the four-stroke engine, two-stroke fuel consumption is higher, overlooking, however, two important factors. Extensive research on the subject of two-stroke scavenging and the associate pressure waves [for the purposes of exhaust pressure wave tuning], has resulted in improving the load-cycle system of the two-stroke engine in such a way that its consumption compares favourably with other types of engines. The best results are obtained with three cylinder two-stroke engines, because with suitable adaptation of the exhaust system, the load cycle process can be particularly favourably influenced. Furthermore, the most favourable fuel consumption level for the two-stroke engine is in the particular load sector, while with a four-stroke engine this is at full load. If the parabolic resistance curve of the fuel consumption for a four-stroke engine and a two-stroke engine are examined it will be noted that with normal travelling resistance, viz. on the level or on small inclines, the parabolic resistance curve of the two-stroke engine passes through the sector of lowest fuel consumption, while with a four-stroke engine this is not the case. For this reason, the consumption of a modern two-stroke engine vehicle will be lower than that of a four-stroke engine [assuming general driving conditions in a generally flat landscape – let’s not consider hills!]. In addition, a very simple means is available which in earlier times had been utilized to avoid any disadvantage regarding cost of fuel for the owner of a two-stroke vehicle - namely free-wheeling. This makes it possible that on long stretches the vehicle can travel without the help of the motor, the latter operating only on no-load consumption. Anyone having so far only used four-stroke vehicles will be able to rapidly learn the somewhat different mode of driving which results from free-wheeling and will no longer want to miss this advantage [editor - as a DKW owner I can attest to advantages of the freewheel. My 1952 Tatraplan is extremely well streamlined, which makes it very fuel efficient, especially given it’s rather low powered ‘industrial-style’ engine. It could be made even more efficient if it had a freewheel, allowing it coast on the inertia of the vehicle and engine without drag effect of the wheels, transmission and engine. I am perplexed that designers of four-stroke engines have not considered implementing this feature in modern cars, with the constant push for improved fuel efficiency].
The lower the yearly mileage, the more the cost of fuel consumption loses its significance compared with other operating costs. For this reason, the two-stroke engine is especially advantageous for all those who use a vehicle primarily for driving to work and occasional trips. As has already been stated, the two-stroke engine is characterized by simple construction and the use of a minimum of moving components, and the simpler a mechanism is designed, the lower will be its requirements for maintenance and repair. It is this aspect which draws users to the two-stroke engine time and again: It needs practically no service attention either in summer or in winter. With a two-stroke engine there is no need to readjust or regrind valves, to frequently change the oil, and there is no work with oil filters. Of course, all the many parts which a two-stroke engine does not require cannot cause trouble or require repair either. The Service network of a company may be as excellent as it can be, it is still better in any case not to have to make use of it. However, when occasional repairs are necessary, the two-stroke engine is again superior, because its construction is so simple that repairs are easy.
When buying a vehicle this represents another important aspect because many users like to do their own maintenance and repair work. Considering its constant state of readiness, the two-stroke engine has a special point to offer during the winter season. It is no secret that the number of motor cars exceeds the available garages by far and among those there are many which cannot be heated. Thus, it can easily be found that during the winter, a four-stroke engine parked in the open cannot be started.
Difficulties arise mainly when the vehicle is used in city traffic, where operating conditions are not favourable for the battery due to the dynamo not receiving sufficient time for recharging. In winter, however, a well charged battery is one of the principal conditions for good starting because the resistance of the cold motor when starting is materially increased by the stiffness of the oil in comparison with a warm engine.
With a four-stroke engine the starting effort is much higher due to the greater number of moving parts involved, and after starting a certain lack of oil will occur because the oil pump cannot move the stiff oil fast enough to reach all vital points. On the other hand, with the two-stroke engine the lubricating oil is sucked in with the fuel-air mixture and thus provides adequate lubrication from the first instant. For this reason, the two-stroke engine can drive off right after starting and thus materially reduce wear during cold-run period. While the advantageous cold starting characteristic of the two-stroke engine is generally acknowledged, its favourable behaviour during warm-running periods are not so well known.
In general practice with the four-stroke engine automatic starting carburettors or carburettor adjustments to provide increased fuel are provided for the improvement of engine behaviour during this period. But both of those measures result in an unnecessary increase of fuel consumption and contribute to increased carbon monoxide production.
Finally, the traffic safety aspect has to be considered also. The statistics of accidents show that during overtaking the occurrence of accidents is particularly heavy. Overtaking becomes more critical with increased traffic density. Here too the two-stroke engine proves it advantage because with the same swept volume higher torque is produced than in four-stroke engines. Besides this, the two-stroke is much less sensitive against excessive speeds These are two important aspects for rapid, and therefore safe overtaking. Summarizing the advantages of the two-stroke engine in comparison with a four-stroke engine, the following emerges: low manufacturing cost, less high-quality materials required, low weight, lower space requirement, practically no maintenance necessary, low repair expenditure, and better starting and acceleration characteristics.
Diagram 1 - Fuel consumption of a small car running at cruising speed on level ground.
If the car is equipped with a three-cylinder two-stroke engine its fuel consumption will be lower in the sector of high-speed travel than with the respective four-stroke engine.
Diagram 2 - Full-load characteristic plotted as specific torque over engine speed for two four-stroke engines and one two-stroke engine.
Superiority of the two-stroke engine is evident. The specific torque value results from absolute torque Md referred to swept volume VH.
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