Thursday, May 17, 2012

Replacing Internal Combustion Engines

First let's look at a common and widespread industrial application for electric vehicles, and how manufacturers and owners eventually settled on a hybridised solution combining batteries with ultracapacitors, to successfully replace internal combustion engine performance in the short-range heavy duty vehicles.
Forklift manufacturers have tested out several technologies over the years in attempts to increase the efficiency of their vehicles. Their success was limited, and they have traditionally settled for batteries as the energy storage system of choice. However, batteries have proven to be less than satisfactory. They are energy dense but not power dense, and they have temperature and lifespan limitations that affect productivity. Increasingly, forklift manufacturers are adopting ultracapacitors in tandem with batteries. Ultracaps are power dense, but not energy dense, and they allow for a lower charge rate, enabling the application to operate at a lower temperature. The result of the ultracap-battery combination: longer lifespan and better performance.

Ultracaps also offer other benefits to forklift manufacturers and AGV owners. In an emergency situation, ultracaps provide enough energy for peak shaving, which lowers the power to a safe and manageable level. In full-crane operations, users need only four megawatts of ultracap banks. Ultracaps also increase the life of the batteries with which they partner; a 3,000 pound lead acid battery partnered with an ultracap can last up to four hours, when alone it would last only one hour. And finally, ultracaps have endured and successfully completed crash tests, meaning they are rugged enough for the nature of the work AGVs do.

Ultracapacitors are particularly useful in dynamic systems where applications perform several accelerations that last just a few seconds. These rapid movements, typical in AGVs, set the stage for energy recapture, which ultracapacitors excel at doing. The high-power and high-energy applications in the AGV market can benefit significantly from a hybridized solution of ultracapacitors and batteries, while seeing a payback on the ultracapacitor investment in just 18 months. _Environmental Leader
This solution will not be enough to replace internal combustion engines (ICEs) for on-road vehicles, due to their lack of range. To replace ICEs for on-road vehicles, a triple-hybrid solution might be best: fuel cells, batteries, and supercapacitors.
Internal Combustion Engines Best Single Power Source for Energy & Power Densities

It is impossible at this time for any single electrical power storage device to match the internal combustion engine for both power density and energy density, particularly when taking expense into account.
Comparing Fuel Cells, Batteries, and Supercapacitor Power Response

As you can see when comparing fuel cells, batteries, and supercapacitors, each has different strengths and weaknesses in terms of supplying power for acceleration, and in terms of storing energy for long range driving between recharge or refuel.
Specific Energy vs Specific Power for Fuel Cells, Batteries, and Capacitors

Energy Management for Fuel Cell - Battery - Supercapacitor Vehicle

This paper proposes a perfect energy source supplied by a polymer electrolyte membrane fuelcell (PEMFC) as a main power source and storage devices: battery and supercapacitor, for modern distributed generation system, particularly for future fuelcell vehicle applications. The energy in hybrid system is balanced by the dc bus voltage regulation. A supercapacitor module, as a high dynamic and high power density device, functions for supplying energy to regulate a dc bus voltage. A battery module, as a high energy density device, operates for supplying energy to a supercapacitor bank to keep it charged. A FC, as a slowest dynamic source in this system, functions to supply energy to a battery bank in order to keep it charged. Therefore, there are three voltage control loops: dc bus voltage regulated by a supercapacitor bank, supercapacitor voltage regulated by a battery bank, and battery voltage regulated by a FC. To authenticate the proposed control algorithm, a hardware system in our laboratory is realized by analog circuits and numerical calculation by dSPACE. Experimental results with small-scale devices (a PEMFC: 500-W, 50-A; a battery bank: 68-Ah, 24-V; and a supercapacitor bank: 292-F, 30-V, 500-A) corroborate the excellent control principle during motor drive cycle. _Abstract of Journal of Power Sources study

Fuzzy logic power management for fuel cell - battery - supercapacitor electric vehicle IEEE Vehicular Transactions

Some manufacturers are attempting to combine the battery and the ultracapacitor into a single device, and others are combining the two into a single sealed package. The advantage of combining the two devices for better total power and energy densities is clear. The addition of the fuel cell to provide much longer range -- providing for fully charged batteries and ultracaps over an extended time -- creates more expense and a more difficult technical challenge, but appears to be the only way of replacing the ICE ultimately.

A future invention which combines the functions of all three devices in one, is not out of the question, and is likely to reduce the cost of the all-electric powerplant eventually, when it can be manufactured as an integrated device.

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