The Two-Cylinder Club

Today, I’d like to discuss a technology used in some vehicles called cylinder deactivation, or variable displacement. It’s a system used in some reciprocating engines that selectively deactivates some of the cylinders to improve efficiency and save fuel. This is generally accomplished by incorporating actuators that hold the intake and exhaust valves open so as to create an “air spring”, which has an equalizing effect on the overall combustion cycle of the engine. A relatively old technology, the closest predecessor to use a design like this was the hit and miss engine, which accomplished the task by holding the exhaust valve open. Several automotive makers have experimented with variable displacement models, having little success. Today, the concept is regaining strength with rising fuel prices and increasing environmental awareness. Some newer engines that were previously deemed “guzzlers” are now being redesigned with selective cylinder deactivation technology as a less costly alternative to a hybrid power-train. One example of this is the newer Chrysler Hemi engine, though I understand from talking to the owners of these that the Fuel Saver mode only kicks in above 65 MPH.

In yesterday’s post I talked about hybrid vehicles. It was my understanding that the engines in hybrid vehicles were directly coupled to the electric motor and deactivated cylinders to “shut the engine off” while still running on the electric motor. I was under the impression that the engine still rotated with the transmission without firing when not in use. I guess I can’t give the auto makers quite as much credit now, as I realize that the engines in hybrids behave much like they do in non-hybrid vehicles with automatic transmissions, stopping the engine completely and restarting with a smaller motor when needed.

I don’t really understand why all vehicles don’t have variable displacement technology. I mean heck, a car or truck only needs one cylinder to idle, not eight. The goal is to use the full potential of each cylinder. At idle or partial throttle there is a vacuum inside the cylinders; in other words, an engine only uses as much air as it needs to. This becomes a problem with larger, multiple cylinder engines because you get pumping loss, inefficiency resulting in low pressure at top-dead-center of the compression stroke. Of course, lower pressure equals lower efficiency. So if at idle we take away 7 of the 8 cylinders in operation, that one cylinder left over has to use much more of it’s maximum power output to maintain operation of the engine. I would gladly take away three of the six cylinders in my car if it meant better mileage, not like I need all six anyway. Diesels could accomplish this even easier, simply by shutting off the fuel to the cylinders that you want to cut, now we’re talking mileage.

I think that all automakers should start designing their vehicles with variable displacement technology. The changes are easy to implement, and the rewards would be great to the consumers. If they just invest a little more time in getting the system right, it could be huge for a form of propulsion that is on it’s way out anyway.

Maybe I Was Wrong About Hybrids

I used to think that hybrid vehicles were a waste of time and energy. It made sense to me that a car that used an electric motor directly inline with the engine would never be efficient and would pretty much always be limited to the efficiency of the engine. If you’re new to the workings of gasoline hybrid technology, I’ll try to bring you up to speed. We’ve all heard of hybrid vehicles by now, they have a gasoline engine that is assisted by an electric motor and a bunch of batteries. There are two types of hybrids, series and parallel. Series hybrids have an electric motor mounted directly to (or basically on the same shaft as) the gas engine. The Toyata Prius and Honda Civic hybrids are the two best examples of these. Parallel hybrids have an electric generator mounted to the engine for the sole purpose of generating electricity for the electric motor that drives the wheels. Big diesel locomotives are a perfect example of this type of hybrid, which in my opinion, is the best type. For more information on hybrids, check out this Wikipedia page.

My big problem with hybrids was the fact that there have never been any commercially produced of the parallel type, they have all been series. This means that the engine still has to run at varying engine speeds depending on the speed of the vehicle, which is inefficient because gasoline engines are most efficient at a set speed and load. Upon researching the Prius, I came across the technical page explaining the Hybrid Synergy Drive. I now realize that vehicles that use this type of powertrain can function as both series and parallel hybrids. They accomplish this with two motor/generators that are connected to the engine and each other by a type of clutch and a continuously variable transmission (CVT). With this setup the engine can run independent of the wheels for the sole purpose of charging the battery, acting as a parallel hybrid. It can also function as a series hybrid by using one of the motors to assist the engine in acceleration and provide regenerative braking. The CVT in combination with the two motor/generators allows the engine to run mostly in it’s most efficient speed and load range. It seems to me, now, that the new technology added to these hybrids has utilized much more of the potential efficiency of gasoline engines, without the extra baggage of a full-out split parallel hybrid.

Despite this great new technology, I still don’t think that gasoline engines are the way to go. Diesel engines are far more thermodynamically efficient than their gasoline counterparts, we’ve known this for a long time. It’s all about the combustion process, compression ignition will always be more efficient because higher compression generally gives higher efficiency. A good running car with a four-cylinder diesel engine gets better mileage than one of the newer gas hybrids. I think we need a vehicle that features a small diesel engine coupled to one of the newer hybrid drive systems. That, in my opinion, would be the ideal hybrid.

Home Bi-generation


It is a known fact that the modern internal combustion engines in automobiles have a fuel-to-wheels efficiency of only about 25%, maybe a little more in the newer hybrid vehicles. In fact, if you are interested in the physics of this I found this article very interesting. The main opponent here is friction. It’s been proven that most of the energy that is converted from fuel in an internal combustion engine ends up as unusable heat. Ever wondered why cars and trucks need that big ol’ radiator in the front? It has to be large enough to remove 600 Horsepower worth of heat from your 200 Horsepower engine, because that is about how much energy is going to be lost as heat at maximum power. Obviously the modern internal combustion engine, though reliable and popular, is not very efficient at producing tractive power.

If our homes need both heat and power, why don’t we just generate them both ourselves.

If we turn the numbers around here, we realize that the internal combustion engine is actually quite efficient at producing heat. If you live in an area the gets cold winters, you might know first hand that automotive engines can produce a good amount of excess heat. I’ve had the window down in my little car in the middle of winter and been perfectly comfortable (even a little warm), while the engine coolant temperature remains unaffected, as if boasting that I can’t cool it down. See where I’m going with this?

If our homes need both heat and power, why don’t we just generate them both ourselves. We have gas heaters with the potential to make electricity, and we have gas generators that make excess heat. A single generator in every home could be used for heat, energy, and other things. The real question here is: would this be more expensive? I guess the answer depends on what kind of device we use. I wouldn’t use an internal combustion engine, they are too loud, inefficient, and not really designed for that length of service. Gas turbines are reliable and great for constant-speed, constant-load applications, but they too are loud and somewhat inefficient, especially on a smaller scale. I think for this one we should go with the proven prime-mover of our energy market: steam. A steam boiler can provide electrical power through a turbine and generator without too much noise or excess waste. The turbine could also provide rotary power for other devices like air conditioning and water pumping. Heat could be distributed through steam pipes and convectors, transferred to a hydronic heating system, or exchanged through a forced air radiator. A loop could even be provided in the system to heat water. Most homes already have a furnace of some sort installed in them, I see no reason that a generator couldn’t take the place of it.

But what about the efficiency of this whole scheme? Well, if we think about the efficiency of the power generated by a coal-fired power plant, which is only about 33% as noted here, it’s not much better than an automotive engine, not to mention energy losses in transmission and various other parasitic losses. With heating boilers becoming increasingly more efficient, up around 95%, I see no reason that a bi-generation system could not be even more efficient while providing cheaper power, heat, and other utilities. This is definitely not a solution to reduce the consumption of fossil fuels, but there is huge potential here for individual power. Also, the existing power transmission grid could be used as a buffer, feeding into the grid when generating, and consuming from the grid when not.

Maybe this is not something that every house and every building in the world should be doing, but for places that are far from other utilities, like cabins, mountainous areas, and deserts, there is some serious potential. Perhaps the urban areas should get their heat and power from a power station, and smaller suburban and country homes should make their own. Just my thoughts, what do you think?

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The Think Blog Is Officially Online!

Welcome and thank you so much for taking the time out of your busy day to visit my blog. Now I know that this page is pretty plain right now, I haven’t spent much time making it look pretty, I’ve been too excited to get my thoughts down in print. This blog is all about making things better, about improving the equipment and gadgets and devices that make our world go ’round. It’s no surprise that in our modern world, products are marketed for the sole purpose of the sale, they are not┬ánecessarily built and designed with reliability and efficiency in mind. There is no specific field or category that this blog will focus on, some articles may be about automotive, others about computers, others about energy production. They will all, however, be about improving designs and processes. Most people don’t really think about how well their engine runs or how efficient their furnace is. That’s where I come in.

If you’d like to know more about me, please see my About Me page. I have a knack for figuring out how to make thinks better, always have. There are so many things in this world that we rely on, yet they could be better. I can think of at least 100 right now, but if you have any ideas or topics you’d like to discuss, feel free to contact me. This post won’t last long, I’ll be writing more very soon, so check back often to find out what the latest topic of the day is.

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