APPLICATION OF DIESEL ENGINES IN CARS

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Front page of Auto Feb 1930

Mercedes-Benz Type Z engine with valve cover removed.

Disclaimer: Some meaning can be lost in translation. Done by Claude.

THE USE OF DIESEL ENGINES IN AUTOMOBILES

(AUTO, Year IX, No. 2)

The ever-growing demand for fuels and the dwindling reserves of gasoline are prompting engineers to seek new ways of building motor vehicles and fuel mixtures to replace gasoline.

France and Germany, as countries with the poorest oil reserves, are naturally most interested in finding new solutions that would enable self-sufficiency and reduce gasoline imports. Both countries have pursued different paths. In France, so-called "gazogeny" (gasifiers) are fashionable today — devices that allow the use of charcoal or wood to power internal combustion engines. In Germany, it is Diesel engines powered by crude oil or gas oils. Both systems can currently be used successfully in trucks and buses, and it is only a matter of a short time before these achievements of modern technology are applied in passenger cars as well.

What does the Diesel engine offer us in a car? First and foremost, fuel savings of up to 80%, and certain design simplifications such as the elimination of the carburetor, magneto, spark plugs, and so on.

How the Diesel Engine Works

Diesel engine, manufactured by Saurer.

Let us briefly recall the operating principle of the Diesel engine. In a normal combustion engine, we use as fuel a mixture consisting of a precisely defined amount of air in which gasoline is dispersed. This mixture, prepared in the carburetor, is drawn into the cylinder, compressed, and ignited by an electric spark. In the Diesel engine there is no intake of mixture, no carburetor, and no electric ignition. Liquid fuel is injected under high pressure into the cylinder filled with compressed air. Since the air has already been raised — due to high compression — to a temperature above the ignition point of the fuel, the fuel ignites by self-ignition at the moment of injection, and the engine runs on this basis.

As we can see, at first glance the operation presents no difficulties and is straightforward, all the more so because for a Diesel drive we can use almost all heavy oils, such as gas oil, crude oil, white and brown paraffin, shale oil, lignite oil, and even palm oil. In reality, the application of Diesel in a car engine has presented, and continues to present, many serious difficulties — an entire series of factories has had their engineers working on this problem for a considerable time. It is also extremely important from an aviation standpoint, as it greatly reduces the fire risk in aircraft due to the absence of electric ignition and the use of heavy, hard-to-ignite oils.

Diesel engines, normally operating in factories as stationary power units, have a whole range of auxiliary operating devices that had to be replaced with others before they could be applied to road vehicles. In addition, normal Diesel engines are slow-running, which was also an obstacle to their use in automobiles.

The 4-cylinder diesel engine of a 6-ton Morlon truck. A Bosch fuel injection pump is visible in the foreground.

The first attempts to increase the number of revolutions in Diesel engines began more than twenty years ago, and parallel to this came efforts to reduce their weight relative to one mechanical horsepower. The result of these efforts was the application of Diesel engines to German submarines. The engines used there were brought to 500 rpm — sufficient for boats, but decisively too little for automobiles. The complex cycle of the Diesel engine discouraged further attempts in this direction, so a different path was chosen: eliminating the compressor. They began to study systems of injecting fuel without a compressor. Two paths were available: one was injecting fuel under high pressure directly into the combustion chamber, the other was injection into a special pre-chamber placed in the cylinder head. After three attempts, the results turned out to be satisfactory, and from that time we see an ever-growing number of trucks with Diesel engines operating in Germany and Switzerland to the full satisfaction of experts.

Despite the existence of a whole series of patents on carburetors theoretically enabling the use of heavy oils in normal combustion engines, to date only the Diesel engine truly enables this. A vehicle with a Diesel engine possesses, in the opinion of all experts, all the qualities needed for a truck: reliability, low weight, good revolutions, and caloric efficiency per unit of power. The great difficulty was in the practical design of a device enabling, in the Diesel engine, the dosing of injected fuel according to revolutions and the rapid combustion of heavy fuel. Dense fuel must pass quickly through the auxiliary devices, and difficulties are again encountered at maximum pressure, which is a function of combustion speed and decreases with reduced engine weight.

The Diesel engine as currently used in automobiles has all the basic engine components made of light materials — such as the crankshaft, pistons, connecting rods, cylinders, etc. — but lacks its most delicate and most difficult-to-regulate organs: electric ignition and the carburetor.

Diesel engines for trucks and buses are currently built by the following German factories: Koerting, Deutz, Limke-Hofman-Boschwerke, Daimler (Mercedes-Benz), M.A.N., Krupp, and Junkers, and in Switzerland by the famous truck manufacturer Saurer.

The Mercedes Diesel Engine (Type Z)

To familiarise ourselves with Diesel, let us examine the construction of the Diesel engine, type Z, produced by Mercedes. There are also other types produced by the same factory, but since they require compressed air for starting, they are more complex and I will omit them here. The Daimler (Mercedes-Benz) type "Z" engine has separate pre-combustion chambers. These chambers are connected by separate channels to the interior of the cylinders. Fuel injected into these pre-chambers partially burns; the pressure created violently throws the exploding mixture into the interior of the cylinder and mixes it with additional air. The pressure of the incoming mixture is about 35 atmospheres; the pressure on the piston after combustion is about 40 atmospheres. These pre-chambers also fulfil the role of a compressor, as they facilitate the entry of fuel into the cylinder, atomise it, and mix it with air.

The injected fuel encounters inside a kind of burner, which serves two functions: atomiser and conductor of ignited molecules. The study of such a burner required extensive experimentation.

The described engine is a six-cylinder with a stroke of 165 mm and a bore of 105 mm. Cylinder capacity: 8,568 cm³. It can reach 70 km/h at 1,300 rpm. The crankcase and two blocks and the cover are made of light metal. Cylinder liners are replaceable, made of grey cast iron. The cylinder head is of cast iron, fitted with intake valves, exhaust valves, and injector valves. The pre-chambers are also located in the head. Valves are controlled from above by push rods and rocker arms. The camshaft is in the engine crankcase. The crankshaft is mounted on seven oversized bearings due to the high loads in the engine. All organs of the Diesel engine are subject to stresses not encountered in normal engines, and their construction therefore required extensive study. For example, the piston had to be so designed as to withstand high pressures and temperatures. The piston itself is of cast iron with an aluminium plate as a heat deflector. Lubrication and cooling are as in normal engines. The injection pump and the fuel supply pump are driven by gears connected to the camshaft. The injection pump is the Bosch system. This pump replaces in the Diesel engine the carburetor and electric ignition; it is positioned so that the driver can operate it easily. Fuel dosing and speed regulation can be controlled by a lever on the steering column and a pedal in the position of the accelerator. Starting the engine is done by means of an electric starter.

The Saurer Diesel Engine

Another very popular Diesel engine is the one produced by Saurer in Arbon, Switzerland. This engine has the following components different from petrol engines of the same purpose:

A 6-cylinder injection pump with 6 Bosch-system nozzles, special combustion pre-chambers, special heaters enabling cold starting, and a special governor that doubles up — checking both maximum engine speed and idle speed. The governor acts directly on the injection pump, just as a governor in a normal engine acts on the throttle.

Each Diesel cylinder has a combustion pre-chamber in the shape of a bomb. It is located in the head and connects with the interior of the cylinder via a funnel-shaped channel. At top dead centre, the piston almost touches the bottom of the head, so the compression volume is actually only within the bomb and the funnel-shaped channel. When the piston moves up, it pushes all the air drawn in through the intake valve into the pre-chamber and into the funnel. This creates a strong air current in the funnel — important for mixing the injected fuel in the pre-chamber with air, especially since injection occurs 15° before top dead centre, and the fuel therefore mixes well with air. After self-ignition the same thing occurs, but lasts longer because the mixture strongly compressed in the pre-chamber supports combustion occurring in the funnel from the cylinder side. The temperature of the uncooled pre-chamber does not exceed, according to factory data, 400 degrees, while the temperature in the funnel is about 1,700 degrees. Combustion in this device is very complete, and the exhaust is clean at any number of revolutions. Even at slow revolutions (300–400 per minute), no smoke comes from the exhaust.

Compression ratio: 15.5; pressure at end of compression theoretically 35 atm, practically 30 atm. Maximum pressure, depending on later or earlier injection, is 36–42 atm. Temperature at end of compression about 500°C, which is sufficient for self-ignition of gas oil, which ignites at 30 atm at a temperature of about 350°C.

The exhaust temperature is somewhat lower than in petrol combustion engines, as it amounts to about 600°C.

The engine has a cylinder stroke of 150 mm, bore of 110 mm, cylinder capacity 8,550 cm³, power at 1,600 rpm of 83 HP, which corresponds to a mean pressure of 5.5 atm. At 1,100 rpm it reaches about 6 atm.

Numerous and precise tests showed fuel consumption of 210–230 grams per HP/hour, calculated at 10,000 calories per kg of fuel:

632 / (0.210 × 10,000) = 0.30, i.e. 30%.

Oil consumption is identical to petrol engines. No lubricant dilution has been found, as is the case in engines with carburetors adapted for spraying heavy oils.

The vehicle has a 225-watt dynamo and a 6 HP Bosch starter. Two 12-volt, 60 amp/hour batteries, each with a magnetic switch that toggles between starting and charging/lighting. Electric heaters placed in the cylinders are heated, when starting cold, by electric current drawn from a separate battery of about 2 volts and a capacity of 80 amp/hours.

As we can see from these two descriptions of Diesel engine applications in trucks, they have taken concrete form, and all the data indicate that diesel trucks will gradually replace petrol-driven ones. The opinion that Diesel engines did not give good results and were less flexible than petrol engines no longer withstands criticism. The benefits of their use — namely savings on petrol in the national balance and in every car owner's pocket — will certainly soon have a wide influence on the widespread adoption of these vehicles. The Junkers company is seriously working on the application of Diesel engines to aircraft and has achieved very positive results in this direction, which promises significant changes in this field.

Stanisław Szydelski

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COST CALCULATION (approximate)

Operating costs of an automobile train consisting of a truck with a 6 BLD (Diesel) engine, capacity 7 tons on 6 pneumatic tyres, together with a trailer of capacity 5 tons on 4 pneumatic tyres. (Factory data of Saurer)

Purchase price ex Arbon:

Item	Swiss Fr.
Chassis	38,050.–
Body	3,350.–
Trailer	8,400.–
Total	49,800.–

Total in Polish złoty: Zł. 86,154.– Customs (chassis): Zł. 6,357.– Customs (trailer): Zł. 860.– Transport: Zł. 1,315.– Total price delivered Warsaw: Zł. 94,686.–

a) Daily fixed costs (constant regardless of kilometres driven):

• Interest on capital (10% of Zł. 94,686): Zł. 31.50
• Driver, mechanic, and garage: Zł. 26.–
• Total: Zł. 57.50

b) Variable costs per kilometre:

• Gas oil consumption: 28 kg per 100 km at Zł. 0.35½/kg → Zł. 0.19
• Oils and greases: Zł. 0.03
• Repairs: Zł. 0.15
• Tyre wear: Zł. 0.43
• Capital depreciation (excl. tyres) Zł. 83,886 over 250,000 km: Zł. 0.34
• Total per km: Zł. 1.05

(Insurance costs not included.)

Operating costs based on daily distance covered:

Daily distance	Total daily per train	Per train per km	Per tonne per km
50 km	Zł. 110.–	Zł. 2.20	Zł. 0.18
100 km	Zł. 162.50	Zł. 1.62½	Zł. 0.13½
200 km	Zł. 267.50	Zł. 1.34	Zł. 0.11
300 km	Zł. 372.50	Zł. 1.24	Zł. 0.10⅓

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This is a fascinating 1930 article from the Polish motoring magazine AUTO, covering the early adoption of Diesel technology in road vehicles — quite forward-looking for its time!