1920 Muncie 5CNA Oil Engine
The oil engine was the lower cost variant of the compression ignition engine. With compression ignition, Dr. Rudolf Diesel had a great idea but at around the turn of the century, the technology was not perfected. “True” diesels were large, expensive and had complex injection systems. They also required a license to manufacture them under the Diesel patent. The door was open, however, to other methods that skirted around the Diesel patent and delivered some of the benefits of a diesel. They were called oil engines.
Oil engines were on the diesel family tree but not technically diesels. There were two varieties, low compression (70 to 150 psi – approximately 5:1 to 8:1 CR) or medium compression (between 150 and 250 psi – up to 13:1 CR, or so). In studying the old texts, the medium-compression oil engines were often called “semi-diesels” and in later years, oil engines were often lumped together under that term. Like the diesel, fuel was ignited by heat of compression but with the oil engine, the fuel had to be heated and vaporized first… sometimes known back in the day as “cracking.”
Typically that fuel heating was done by a hot spot in the combustion chamber. These hot spots came in many forms, from bulbs to tubes (so-called hot bulb and hot tube engines) and other types. On a cold, or even cool, start, external heat was applied to the hot spot, heating the combustion chamber so that when fuel was injected, it instantly vaporized so it could be ignited at the lower compression ratios.
When the engine was under load, the hot spot was designed to retain enough heat so that combustion could be maintained. The hotter it was, the better it ran… and vice versa. Typically, a kerosene torch was use to heat the hot spot and how long you had to do that depended upon the ambient temp, the condition of the engine and the lightness of the fuel (heavy oil took more heat).
Oil engines had a heyday from the turn of the 20th Century into the mid 1920s. They were still manufactured into the 1930s when true diesels, and their huge advantages in efficiency, became affordable and practical. What kept the oil engines strong in the market was their simplicity and low cost, as well as their ability to run on low grade fuel oils.
Muncie Oil Engine Company
The Muncie Oil Engine Company started in 1901 as the Muncie Gas Engine & Supply Company in, you guessed it, Muncie, Indiana. It began with the acquisition of the Auglaize Machine Company of St Marys, Ohio, by a group of Indiana investors. Auglaize was already an engine builder and had several recent engine patents. It’s known they built a number of gas engines, some of which have survived. One of those patents involved an incandescent igniter of a type that might have worked for an oil engine. There are various references that indicate some engines may have been built between 1901 and 1910 under the Auglaize name but 1910-11 is when the Muncie Oil Engine began to be seen in period advertising. During that period, the company moved from Ohio to Muncie, Indiana.
Muncie Gas Engine & Supply first advertised the Muncie oil engine by claiming it could run on crude oil, fuel oil, gas oil, kerosene or distillate. Just a year later, they advertised oil engines from 10 to 100 horsepower. They claimed their 25 hp engine could run 10 hours at a full load on fifty cents worth of fuel. The Muncie engines were two-strokes and used a hot bulb design some period engineering texts regarded as one of the superior designs of the era. The Muncie designs evolved and by 1920, the range of engines was from 10 to 125 horsepower.
The featured engine is a 1920 Model 5CNA, type C, which made 55 horsepower at 250 rpm from a 12 x 19 inch bore and stroke. This engine is an electric special, designed to run generators. The main difference in that designation is dual flywheels, versus a single, and the means to couple it to generators. The 1921 catalog lists the 5CNA as being rated to run a 36 kilowatt generator.
Muncie Oil Engine Company was all over the pages of the commercial publications until 1924, when it suddenly disappeared. Why that happened seems lost in the research we were able to do of that period. By then, the oil engine was certainly past it’s prime and other more efficient types of engines had reached their price point and delivered similarly low operating costs. This engine is owned by the Tri-State Engine and Tractor Association and has been a big part of their annual show since it was restored in 1994.
Here is the Muncie hot bulb combustion chamber and it shows the way combustion works in a crankcase-scavenged oil engine. This is from an old manual to which we added the colors of blue for intake and red for combustion and exhaust. In case you hadn’t figured it out, the chamber to the left is the hot bulb that gets heated for startup.
Atmospheric pressure alone isn’t enough to fill the cylinder of a two-stroke and a pump is needed. The simplest answer back in the day was to use the piston and a sealed crankcase in a process called crankcase scavenging. Look first at #1, where the piston is nearing TDC and the injection process has begun. The bulb is very hot, either from previous combustion events or external heat, and the fuel is vaporizing. The additional heat of compression increases the air temperature enough to create ignition and that takes us to #2. Combustion has happened and the piston is moving down the bore.
In #3, the piston has moved down the bore, uncovering the exhaust port to release the high pressure combustion gasses. The piston moving down the bore has also reduced the volume of the chamber and created 3-4 psi pressure in the crankcase. The spring-loaded inlet valve on the stack is closed and the inlet port is not yet uncovered.
Now look at #4. As soon as the intake ports are uncovered by the piston, air is pushed into the cylinder and for the brief time both the intake and exhaust ports are uncovered, the air also helps scavenge the exhaust. Note the flow director on the piston, which directs the fresh air towards the bulb end of the combustion chamber. As the piston reaches BDC and starts moving up the cylinder again, the intake port is covered, then the exhaust, and the cycle begins anew.