More than 9 years ago we received an order from DB Cargo AG to develop an auxiliary power unit for a certain series of locomotives. The task of the aggregate is to generate power and heat when the main engine has to rest. During long idle times in stations, for example.
A classic "auxiliary power unit" in other words.

The challenges were:

Little space, a lot of power and diesel as fuel.

Our customer had already determined that this task could not be realized with conventional reciprocating engines due to the small installation space. That's why we came into play. Our Wankel engines are much smaller and lighter than conventional diesel engines with the same power output. In addition, we are the only company in the world to offer marketable Wankel diesel engines. Thanks to years of research and development.

8 years later, we have delivered almost 80 systems to equip more locomotives.

We would also like to say "thank you" to DB Cargo. Thank you for your trust and loyalty.

P.S.:
So-called Auxiliary Power Units are often also found in aircraft, tanks and boats.

The Wankel engine is gaining a sad notoriety in the current Ukraine-Russia conflict.
One of the positive features of the engine is its small size with high performance. Therefore, the engine is popular for operating unmanned drones. This is also the case with the Iranian drone "Shahed-131", the smaller variant of the "Shahed-136". The "Serat 1" Wankel engine is used. This is a copy of the "MDR-208" from the Chinese company Beijing Micropilot Uav Control System Ltd. This in turn is a replica of the "AR 741" Wankel engine from the British company UAV Engines Ltd.

All three variants share the same specifications:
One rotary piston, 208 cc displacement, 38 hp, gasoline fuel and about 10 kg weight.
This powers a propeller that can provide the drone with a range of up to 900 km.

Unfortunately, many components, including the engine, are available on the open market, so the total cost of a drone is estimated at only $20,000-30,000.
We suspect that the production costs for the "Serat-1" motor variant would be massively reduced by not using special coatings and materials. Only through these would the motor achieve a long shelf life. However, long durability is obviously not necessary for the Kamikaze drone. In the end, we are left with a simple engine design, with relatively few individual components, requiring only aluminum and steel.

We hope that the war, in the Ukrainian sense, will soon be over. And that the Wankel engine will find even more application in civil and sustainable areas.

Due to their design, Wankel engines are far lighter, more compact and simpler than classic reciprocating piston drives. There are no reciprocating pistons, cranks, valves, rods or other complex parts prone to failure. Rotary motors contain only three moving parts, making them more reliable, durable and easier to maintain than traditional internal combustion engines. In addition, these moving parts rotate continuously in one direction, ensuring higher operating speeds, simplified balancing and low vibration. Thanks to their unprecedented weight-to-power and size-to-power ratios, Wankel engines are used in a variety of applications, from light aircraft to power generation to boat and ship building, as well as range extenders for electric vehicles.

One of the disadvantages of rotary piston engines is their low thermal efficiency. The long, thin and moving combustion chamber results in relatively slow and incomplete combustion of the fuel-air mixture. This results in higher carbon emissions and lower fuel efficiency compared to gasoline engines. However, this problem becomes an advantage with the switch to hydrogen operation.

Another weakness of Wankel engines relates to rotor and apex sealing. Poor sealing between the edges of the rotor and the housing - for example, due to wear or insufficient centrifugal force in the lower speed ranges - can cause combustion gas to escape into the next chamber.

Since combustion takes place in only one section of the drive, there is a high temperature difference in two separate chambers. The resulting different expansion coefficients of the materials involved lead to a suboptimal rotor seal. Oil consumption is also a problem, as oil must be injected into the chamber to improve lubrication and keep the rotor tight.

How does a Wankel engine work?

The Wankel engine is an internal combustion engine in which one or more triangular-shaped circular pistons convert the pressure generated during combustion of the fuel-air mixture into kinetic energy. The gas volumes transported in the spaces between the rotor flanks and the housing pass alternately through four different phases: a) intake phase; b) compression phase; c) expansion phase; and d) exhaust phase. These stages are referred to as strokes and make the Wankel engine a four-stroke engine, similar to the Otto reciprocating engine.