Technology – kemrex.de

Technology at a glance

The KEMREX Range Extender is perfectly suited for the rotary engine technology
Battery Rightsizing: KEMREX is five times smaller and twice cheaper than an auxiliary battery
E-Fuel as Alternative for 100 Procent CO₂-Neutrality
Designed for Hydrogen fuel cell as a future option

Perfect application for rotary engines

The KEMREX electrical power generator unit is composed of a multi-fuel rotary engine, a generator, HV electronic components and various controllers. The unit generates HV DC power that is fed directly into the battery. The rotary engine is not mechanically attached to the drive wheels and is only used to generate electrical power. The engine always runs at a constant speed and the RPMs are set and maintained at the optimal performance point with the highest efficiency. This ensures minimal fuel consumption and an optimized exhaust emissions.

Why Diesel?

Our current focus is on the serial production of the KEMREX power unit with a diesel rotary engine. The rotary engine technology is a perfect fit for the electrical generator turning at constant speed and the rotary engine has significant size and weight advantages over the conventional piston motor. With a power output of 18-20 kW, the range extender can nearly double the capacity of a typical e-Truck battery and the unit weighs only 250 kg instead of 1100-1150 kg for a comparable Li-Ion battery pack.

What is Battery Rightsizing?

The KEMREX Range Extender is the key enabler for "Battery Rightsizing". Just installing a bigger and bigger battery to get more range is not always the best or even a viable answer. Established OEMs in the passenger car segment (for example: Mazda) have already moved in the direction of "Battery Rightsizing" and this principle will define the optimal battery size per vehicle for each generation of battery cell technology. According to the "Battery Rightsizing" principle there is an optimal battery capacity for each vehicle type based on the vehicles physical size and weight constraints. Installing a larger than optimal battery is actually counterproductive since the additional size and weight cancels out most or all of the theoretical extra range potential.

If the optimal battery capacity does not alone provide enough range for the customer application, then the vehicle must have an additional energy source onboard. For commercial vehicles, stationary charging time is lost deployment time and the battery electric vehicle must have a mobile power unit like KEMREX onboard in order to truly replace a comparable conventional diesel vehicle.

The optimal battery size for a 12 ton distribution logistic truck with the currently available battery cell technology is between 120 – 140 kWh. Unfortunately, the daily tour for a typical City logistics application requires almost twice that much energy. This is where the range extender offers the ideal solution.

Range Extender vs. additional battery

The energy needed for the additional range can come from additional Battery packs or from a range extender – but the range extender has significant advantages. The KEMREX power unit is smaller lighter and less expensive than an equivalent battery pack. For 120 – 160 kWh of energy, the range extender saves almost half of the 75.000 € in costs and over 75% of the weight of an equivalent batter pack. Even if the energy density of a Li-Ion battery improves dramatically over the next 10 years, the KEMREX range extender will still maintain its advantages and remain the better option.

Multi-Fuel motor vs. Hydrogen fuel cell

The KEMREX range extender is currently equipped with a multi-fuel combustion engine that can burn eFuels, hydrogen or standard diesel. The best option in the short term for a fuel as energy source is – surprisingly enough – Diesel. Diesel ist not only universally available – it is still the fuel with the highest energy density in the vehicle segment – 100x higher than a Li-Ion battery and 5x higher than Hydrogen (even at 700 bar) . The KEMREX design is also flexible enough to allow the integration of a hydrogen fuel cell in the future instead of the rotary engine. The current problems with producing, distributing and storing Hydrogen make this option unattractive at the current time.

Rotary engine vs. reciprocating piston motor

The multi-fuel motor in the range extender is a rotary engine and not a conventional reciprocating piston engine (RPE). This is a key innovation and possible because, as opposed to the drive motor which is exclusively handled by RPEs today, the electrical power generation application fits perfectly with the strengths of the rotary engine design. The power generator requires constant speed operation and this rotary engine is most efficient under these conditions. In addition the rotary engine is smaller, lighter and quieter than a corresponding RPE.

Zero Emissions with KEMREX

The E-truck from Knapp e-Mobility has a 100% battery electric drive system and drives as a zero emission vehicle in regulated zones. When the combustion engine in the range extender is running on synthetic e-fuels, the entire vehicle is CO₂-neutral and the battery is charged “on-the-road” to achieve more range. Even if the customer chooses to run the KEMREX Range Extender on conventional Diesel fuel, the E-truck will reduce CO₂-emissions in comparison to a conventional Diesel truck by 80 und 90 Percent. Since the battery electric vehicle alone does not have enough range to cover the typical daily tour distance – it is not capable of replacing the Diesel truck at all and hence this “Option” saves no CO₂ at all.

Even if the battery cell technology improves from year to year - there are thousands of applications with tour distance requirements than can only be solved with the range extender. E-Trucks with KEMREX enable Customers to replace conventional Diesel trucks now – in real world applications, and with significant savings in CO₂-emissions.

Innovative “green” Drive systems

The rotary engine can efficiently burn more than just diesel which in turn opens new options for CO₂-neutral vehicles. The rotary engine can also run on synthetic e-fuels or on Hydrogen (“green H2”). Future models of the KEMREX power unit can also have a fuel cell instead of the rotary engine. Of course there are still a number of challenges surrounding Hydrogen that need to be answered before it can go into practical use – but thanks to the robust design, the KEMREX unit remains flexible for the future.