Pretty much all modern engines run active knock sensors which finely tune the engines ignition timing in to prevent detonation ! Nuclear Reactor Engineering: Reactor Systems Engineering,Springer; 4th edition, 1994, ISBN:978-0412985317, W.S.C. The basic reasons why an engine can result in knocking includes: Ignition delay inside the injectors. The Cookies Statement is part of our Privacy Policy. 38%. The engine knocking can be reduced by using high-octane fuel, which increases the gasolines resistance to autoignition. To keep it running in tip-top shape, you need to use high-octane gas, which is more expensive than regular unleaded gas. The octane number is actually the simple average of two different octane rating methods motor octane rating (MOR) and research octane rating (RON)that differ primarily in the specifics of the operating conditions. Well, high compression is why a lot of performance engines need premium fuel, or high-octane gasoline. Then again, if your car is making knocking and pinging noises, it can be a good move to try a gas with a higher octane rating. If you 'zero' deck the block and use -12cc dish pistons on, the 383, you will have about 10.3 static CR. See how the piston moves up during that compression stroke? An engine knock is when the air-fuel combustion doesn't happen at the optimal time in the piston's stroke. According to Arman, knock sensors are so-called piezo-electric microphones bolted to the engine block. US spec Propane (Commercial grade vs HD-5) has a CCR somewhere around 12.5:1, and again, this depends on the purity of the fuel, usually between 90 and 95% propane, the balance being propylene, ethane, butanes, and other minor fractions. Knocking is bad; it reduces torque and can cause irreparable damage to your engine. Like we learned on the previous page, static engine compression is measured when the air intake valve of an engine is fully closed. The current practise with CNG conversion is to maintain the compression ratio ( due to dual fuel use), the result is loss of power and efficeincy when using NG. Which brings us to the octane ratings in gasoline. What's the difference between torque and horsepower? What's the highest compression ratio you can run on pump gas (i.e. The best answer of those came from Dr. Andy Randolph, Technical Director at ECR Engines. "The same is true of a piston moving in the cylinder," he says. The ideal compression ratio is as high as possible for the best thermodynamic efficiency. Like static compression, a higher compression ratio means more efficient fuel use and better fuel economy. It increases by increasing the stroke length. Oil temp was 190-200 when running fairly hard. Is premium gasoline really better for luxury vehicles. The compression ratio in a gasoline-powered engine will usually not be much higher than 10:1 due to potential engine knocking (autoignition) and not lower than 6:1. What is compression ratio? When the air is compressed, you get a more powerful explosion from the air-fuel mixture, and more of the fuel gets used. Here is a simple example of how to calculate your compression ratio. Efficiency depends on compression ratio. Proper Fuel Based On Compression Ratio Click ahead to discover what compression ratio is and how an engine can alert you to knocking and pinging. John is building a Nissan 240SX rally car into which hes swapping a SR20VE four-cylinder, currently making about 250 horsepower at the wheels from just 2.0 liters. I asked if this is why we dont see people arent running around with engines that have significantly higher compression ratios than anything we see today. When fuel injector fails to completely ignite the fuel. Have you noticed the wave of cars with great gas mileage hitting the market? Oct., 2003 (Dec. 15, 2011). John laughed. My set up uses a 'zero' deck block, Speed Pro hyper -12cc dish pistons, TF aluminum 64cc heads, 0.039 FelPro head gasket, and a CC XE274 flat tappet hydraulic cam. There are indications that thermal efficiency reaches a maximum at a compression ratio of about 17:1 for gasoline fuels . J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1. Put the octane value has to be found emperically from the lab, not by ignition temperature. The higher the octane number, the more compression the fuel can withstand before detonating (igniting). The higher the piston is in the bore when combustion begins, the more force will be exerted. In general, turbocharged or supercharged engines already have compressed air at the air intake. clearance volume. And just what is high-octane gasoline and why do so many filling stations and oil companies push it so hard? There are also . If you want to get in touch with us, please do not hesitate to contact us via e-mail: The compression ratio in a gasoline-powered engine will usually not be much higher than 10:1 due to potential engine knocking (autoignition) and not lower than 6:1. The more tightly this mixture fits, the better it burns and the more energy is converted into power for the engine. Increasing the compression ratio of an engine design is not possible beyond a certain degree. shoot a burst of rich fuel around the igniting spark plug in an otherwise lean mixture. A . Normally up to 12.to 1 compression ratio, you can get by with 92 or under. A more excellent compression ratio, for as from 12:1 to 14:1, indicates more efficient combustion. Compression ratios in the range of 12 to 20 are typical for diesel engines. It shows, visually, whats going on in your engine as it burns gasoline. And the so-called compression ratio -- and each engine has its own ratio -- refers to just how much of that fuel and air combination the piston compresses. But, a high compression engine has its drawbacks, too. For addressing these issues, Gasoline compression ignition (GCI) engine technology is being developed, which is a futuristic engine technology that takes advantage of higher volatility, and higher auto-ignition temperature of gasoline and higher compression ratio (CR) of a diesel engine simultaneously to take care of soot and NOx emissions . Main purpose of this project is to help the public learn some interesting and important information about engineering and thermal engineering. This website does not use any proprietary data. what you want is a dynamic compression ratio of 8.0:1 to run 87-octane pump gas. The better mixing of air and fuel with each other makes it homogeneous. Vizard, David. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1. Since the temperature attained by the fuel-air mixture during the compression increases as the compression ratio increases, the likelihood of autoignition increases with the compression ratio. Higher compression ratios and combustion efficiency resulting in more power from less fuel and fewer exhaust emissions. So then you can derive the relationship between thermal efficiency and compression ratio, like MIT plotted on its web page and shown above. In the diagram above, that lower 1-2 curve shows the compression stroke. There's another type of compression ratio that takes the opening and closing of the intake valve into account. The compression ratio (CR) is defined as the ratio of the volume of the cylinder and its head space (including the pre-combustion chamber, if present) when the piston is at the bottom of its stroke to the volume of the head space when the piston is at the top of its travel ('top dead centre', tdc). Those are all things we can control and so are the items on our list, all of which are right there inside the cylinder exerting their influence on compression ratio. Thats good for power and also miles per gallon. Tests were conducted on a . The best combustion efficiency is obtained at = 2.00 for diesel and = 1.12 for spark ignition (gasoline) engines. Octane ratings are a measurement of a gas's ability to resist detonation. Anker is launching a new power station in its lineupthe Anker 767 PowerHouse. To illustrate what is happening here, Nielsen says to think of a bicycle. In this work, the authors reviewed engine, vehicle, and fuel data since 1925 to examine the historical and recent coupling of compression ratio and fuel antiknock properties (i.e., octane number) in the U.S. light-duty vehicle market. "As the piston moves down the cylinder, it draws in 500 cc of air and fuel. The Mazda3 with the SkyActiv engine can get 42 miles per gallon (17.9 kilometers per liter). Everyone wants to get a good price per gallon, but is it more cost-effective over the long-term to shell out a little more for premium gasoline each time you fill up? 10.3 static, 8.3 dynamic CR. burgerMemberfrom burbs. Octane ratings are, as this How Stuff Works article points out, a measurement of the gasolines ability to resist detonation. Automotive engineers can improve fuel efficiency and fuel economy by designing engines with high compression ratios. But in other cases you'll never even hear a thing because a knock sensor has already corrected the problem. In order to feel a little more comfortable that the nozzle you select is the right one for both your vehicle and your wallet, it's helpful to understand terms like compression ratio and octane ratings. So what makes their fuel economy so good? With the pistons I have on my 347 I can get 10.9:1 with a 58cc combustion chamber, 10:3:1 with 61cc and 9.9:1 with 66cc. Put another way, youre turning more of your input energy into work. 46%. Interesting idea! Tuning would be very interesting. The type of compression ratio we've just learned about is what's known as a static compression ratio. Youd be getting more pressure in the cylinder and on your piston from the heat input from combustion. K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4. All John has to thank is its very high 14.5:1 compression ratio. For those who either never learned it or have forgotten, it's useful to know: Cars' internal combustion engines all function pretty much the same way. The compression ratio depends on the following parameters: 1) Stroke length The engine stroke length is the length of the combustor or the distance between the bottom dead center and the top dead center of the engine cylinder. Introductory Nuclear Physics, 3rd Edition, Wiley, 1987,ISBN:978-0471805533, G.R.Keepin. Mazda runs 13/1 compression and Ferrari as high as 14/1. Most gas stations offer three grades of octane, with regular rated typically at 87, mid-grade at 89 and premium at 92 or 93 [source: Federal Trade Commission]. In an ordinary gasoline engine, the compression ratio has its limits. For example, if an engine running on gasoline has a . Compression ratios usually range from 8:1 to 10:1. John said that anything over 14.5:1 compression ratio would run the risk of auto-ignition, and it could shoot out a rod or spin a bearing. We'll talk about that on the next page. Its written out and said as a ratio. In order to generate the most power, the optimum approach is to apply downward pressure at the top of the stroke and apply an even amount of pressure to just about the bottom of the stroke. The compression ratio is the ratio of the volume of the cylinder and the combustion chamber when the piston is at the bottom, and the volume of the combustion chamber when the piston is at the top. 2) You may not distribute or commercially exploit the content, especially on another website. This engine produces 84 bhpand requires premium fuel. Efficiency = 1 - (1/compression ratio)^gamma-1 where gamma = ratio of specific heats at constant pressure and constant volume of the working fluid ( for most purposes air is the working fluid, and is treated as an ideal gas ). Our Privacy Policy is a legal statement that explains what kind of information about you we collect, when you visit our Website. In essence, there's more space for the air, so the engine loses some of the power from the air-fuel combustion. Let's say you are compressing a gas with a ratio of specific heats of 1.3 (see ratio of specific heats box below) from a suction pressure -0.5 psig to a discharge pressure of 35 psig. Glasstone, Sesonske. It must be remembered that for all practical purposes 14 to 1 should be considered the maximum usable compression ratio in modern short stroke automotive type engines. Heres Jason Fenske of Engineering Explained breaking down that relationship between compression ratio, heat transfer and efficiency: Anyway, the point is that thermodynamics dictates that thermal efficiency goes up with compression ratio, as you can see by that plot and equation above. The standard recommendation for street engines running on pump gas has always been to shoot for a 9.0:1 to perhaps 9.5:1 compression ratio. Dec. 16, 2011. Jamie Page Deaton The whole thing works on two ideas. 94%. 66%. Most of the modern spark ignition (gasoline) engines have compression ratios between 8 and 11, while compression ignition (diesel) engines have compression ratios in the range 12 to 24. . The 4-1 line shows heat rejection from the gas to the surroundings as the pressure returns to ambient with the exhaust valve opening up. Thats all the air and fuel getting compressed in the cylinder. Its healthy and good for the soul. Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988. That kind of uncontrolled combustion is called knocking. And get this: Even though these cars get some of the best gas mileage in the industry, they're not using gasoline-electric hybrid technology, alternative fuels or other green tricks. To do it, you use the stroke length and the connecting rod length to determine the position of the piston when the valve is fully closed. To be more specific, a piston compresses the fuel and air mix in the combustion chamber of the engine. A gasoline compression ignition (GCI) engine was proposed to be the next generation internal combustion engine for gasoline. He explained that metal simply cannot withstand such high levels of stress, and a compression ratio like that would run things so hot that itd blow up any current engine. February 2009. Average Engine Compression Ratio Compared to Average Gasoline Octane Rating, 1925-2015; Year Average Compression Ratio for New Light Vehicles Average Octane Rating (AKI) Year Average Compression Ratio for New Light Vehicles Average Octane Rating (AKI) 1925: not available: not available 1971: 8.64: 90.08: 1926: not available: not available 1972: . High compression increases your risk of knocking, which is why very high compression engines run high octane race gas or (more commonly now) E85. The engine knocking can be reduced by using high-octane fuel, which increases the gasolines resistance to autoignition. Whats also interesting is that you cant just make an engine with as high a compression ratio as you want. "When a cylinder detonates, the fuel burns at supersonic speed and releases its energy too fast, kind of like a fast stomp on the bicycle pedal.". It's easy to find what octane rating a gas has: Stations are required to post them on bright yellow stickers on each pump. The first of a wave of new high-compression and variable-compression engines from Mazda, Nissan/Infiniti and Toyota, the Mazda has the highest compression ratio in the business right now, at 14:1, which is why it can manage high fuel economy and power figures even without a turbocharger. 10 Ways to Proactively Protect Your Engine, 5 New Engine Technologies That Make Cars More Fun to Drive. The CR varies according to the length of the stroke. First we'll explain the theory behind the compression ratio, so what it is and how it . 29 December 2011. When the piston is at the lowest point, thats called Bottom Dead Center. As you can see, the compression ignition (diesel) engine, at stoichiometric air fuel ratio has a very low combustion efficiency. Please copy/paste the following text to properly cite this HowStuffWorks.com article: Each engine has its own compression ratio. K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2. Chris Warren Federal Trade Commission. Addison-Wesley Pub. If a gas-powered vehicle gets 30 miles to the gallon, a comparable diesel-powered vehicle will get anywhere from 37.5 to 40.5 miles per gallon. Dec. 13, 2011. Remember, under normal circumstances the compressed air and gas mix is ignited by a spark plug. The compression ratio is the ratio between two elements: the gas volume in the cylinder with the piston at its highest point (top dead center of the stroke, TDC), and the gas volume with the piston at its lowest point (bottom dead center of the stroke, BDC). K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2. (b) What If? Here's the good news: You don't have to know anything about the functioning of your engine to make sure you're putting fuel with the right octane rating in your tank. Best Compression Ratio. 85%. (Dec. 16, 2011) http://www.popularhotrodding.com/tech/0311_phr_compression_ratio_tech/index.html, Special Offer on Antivirus Software From HowStuffWorks and TotalAV Security, 5 Ways Modern Car Engines Differ from Older Car Engines. 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