With all these ways that people are trying to save fuel these days, there are a few options that nobody even considers anymore. Sure modern technology is popular and the more electronics the better (or at least that’s what manufacturers seem to think), however there is something to be said about going back to tried and true technology to the past. So the question for this time is probably on your mind right now. “What the hell is he talking about?”
So much energy is lost in an automobile that maybe 10 to 20 percent is actually used to power the vehicle. Most of the chemical energy is lost in the form of heat that is radiated out of the vehicle from the cooling system, and some heat is lost through the exhaust system. But strangely enough, there is some energy that is converted to lost kinetic energy in the exhaust system as well. Kinetic energy is simply put, the energy in a system or object that is in motion. In an automotive exhaust system, the gasses from the combustion cycle evacuate from the cylinder head with a great force that on some vehicles is harnessed by a turbocharger or turbo (technical name: turbo-supercharger), and that energy is used to drive an air compressor. This air compressor forces air into the engine and therefore boosts it (creates an artificial atmosphere). This increases power, but unfortunately under heavy loads also increases fuel consumption. However, off boost, the turbo still spins free and helps the engine breathe, reducing pumping losses and increasing fuel economy. But taking a page of our history and applying it to modern automotive systems would help us conserve even more fuel. I am talking about turbo-compound units.
To understand how these devices work, one must understand turbocharger technology first. The turbine side is very similar, however instead of the turbine driving an air compressor to force feed the engine, it drives a transmission that directly applies power back to the crankshaft. Therefore, the kinetic energy that is normally lost through the exhaust system is recovered and directly recycled into engine power. This means that the power is, with very little losses, free and requires no extra fuel to be consumed. In fact it can even increase fuel economy due to the reduced load stress on the engine. Back in the 1940’s there were a few engines that were produced for military aircraft that had turbo compound units. One of which was the Allison V1710-E22 that was a 4 stroke V12 that made a military power rating of 2320 horsepower, and an emergency rating of 3100 horsepower. Now the most powerful V1710 without a turbo compound unit made 1475 horsepower in the P38. Another engine that was produced, and in much larger numbers was the Curtiss-Wright R3350-TC. This was a radial engine with 18 cylinders that was used on DC-7’s and some Lockheed Constellations. This engine produced somewhere between 3500 and 3800 horsepower, and was capable of flying some 20-30 percent longer than the R3350 without the turbo compound unit (which only produced 2700 horsepower). These are a couple of examples of how power can be increased, and strangely enough, so can fuel economy. (range).
So how does this fit into our modern world of automatic transmissions, hybrid power drives, and electronic engine management? Well, the best part about the turbo compound system is its ability to add power with no internal changes to the engine, and only minor changes to the engine management system. Sure there will be a cost to adding this type of system to any given engine, however the cost cannot possibly be more than a hybrid power drive with all the electronics and batteries. After all we are talking about a completely mechanical system that increases fuel economy about as much as a hybrid does. Under mass production, the cost of these parts will decrease to affordable levels. Now if this is to be a completely feasible technology, we might as well make an industry standard type transmission for the compound drive unit., or at least standardize the dimensional measurements. Therefore input speed from the turbine would be static and output speed to the crankshaft would be static as well (relative to the crankshaft speed). Depending on the size of the engine, the turbine could be any size with any operational speed. So in order to sync the turbine speed to the input speed of the compound transmission (which acts as a torque multiplier), the turbine would be equipped with a simple two or three gear reduction output drive, depending on turbine size and operational rpm. The advantage to this approach would be a standard type compound transmission with greater parts availability, and higher torque capacity. The turbine with output reduction would be a low torque system that would be lubricated by engine oil feed shared with the turbine. Separating these parts would allow easier service on both major components of the system. If a turbine fails, it can be replaced without replacing the compound transmission.
Additionally, the turbine can also be used to power a supercharger as well. This is something that was common on aircraft engines as well. So you also have traditional turbo-charging capabilities in place. Other possibilities include drive power available for high speed alternators and with another reduction drive, it could even run air conditioning pumps or power steering units. The energy that is lost in the exhaust system is a largely untapped resource that if exploited can increase engine efficiency, and reduce fuel consumption while providing more power than ever before. Because of it’s ability to increase fuel mileage it also may be possible to run on E85 ethanol fuel without the fuel economy penalty that comes with its lower potential energy capabilities. Imagine a clean burning fuel with little or no mileage penalty that almost eliminates our dependence on imported oil. So if we lose 15 to 20 percent of our range due to the lower fuel economy of E85 then it can be made up for by turbo-compounding the vehicle.
So all we need is a simple and effective way to transfer turbine energy to the crankshaft. Now, obviously each individual manufacturer will decide to do this in their own way. However I have some ideas that would allow for a much better, more streamlined industry changeover. First of all, each compound transmission would be a standardized unit, at least in dimensions. For example, outside dimensions would be standardized at say 200mm X 200mm X 300mm. All bolt locations and thread pitches would be standardized as well. Also, the compound transmission would be a standard 10:1 rpm reduction unit. All these standardizations would be necessary to allow for part availability and ease of service. Japanese companies would simply have Aisian produce theirs, European companies would have ZF produce theirs, Ford would most likely make their own, and GM and Chrysler would probably have New Process make theirs. Each one would have its own characteristics, but they would be interchangeable. Now, the turbines would each be sized for the engines to provide the most energy to the transmission. They would come with a primary drive reduction to reduce turbine speed to the necessary input drive speed of the compound transmission depending on the size of the turbine. For example if a turbine has an operating range of 250,000 rpm, it would need more of a primary reduction than say a turbine that was for a larger engine that had an operating speed of 175,000 rpm. They would have built in reduction drives that would allow them both to use the 10:1 compound unit. In this way, if a turbine failed, it can be replaced separate from the compound transmission. To me this seems to be the most sensible solution. Each manufacturer would have their own way to attach the output from the transmission to the engine, but the majority of the parts would be interchangeable.
To allow for a slight stall up capability to allow for greater torque production down in the lower (engine) RPM range, the output of the compound unit to the crankshaft would also be allowed to incorporate a flexible drive system like a small torque converter with a lockup function or a fluid coupler. Or a viscous coupler. This would allow for the turbine to spin up faster than crankshaft speed and apply higher torque and then stabilize as crankshaft speed increases.
So this is my idea of how to save fuel in the future. No complex electronic systems, no battery packs, no hazardous materials. More power and better economy, as well as light modifications to existing models. The real question is why hasn’t the automotive industry tried this yet?