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29-456: The 2.0 L (1,998 cc) QR20DE produces 140 PS (103 kW; 138 hp) at 6000 rpm and 200 N⋅m (148 lb⋅ft) at 4000 rpm. The bore and stroke is 89 mm × 80.3 mm (3.50 in × 3.16 in) and a compression ratio of 9.9:1. The QR20DE was replaced with the MR20DE engine in most applications in early 2005. Vehicle applications: The QR20DD

58-566: A turbocharger or supercharger ) is used, the compression ratio is often lower than naturally aspirated engines . This is due to the turbocharger or supercharger already having compressed the air before it enters the cylinders. Engines using port fuel-injection typically run lower boost pressures and/or compression ratios than direct injected engines because port fuel injection causes the air–fuel mixture to be heated together, leading to detonation. Conversely, directly injected engines can run higher boost because heated air will not detonate without

87-400: A compression ratio of 14:1 to 16:1. In a piston engine , the static compression ratio ( C R {\displaystyle \mathrm {CR} } ) is the ratio between the volume of the cylinder and combustion chamber when the piston is at the bottom of its stroke , and the volume of the combustion chamber when the piston is at the top of its stroke . It is therefore calculated by

116-403: A dynamic compression ratio similar to an engine with lower compression but earlier intake valve closure. Forced induction In an internal combustion engine , forced induction is where turbocharging or supercharging is used to increase the density of the intake air. Engines without forced induction are classified as naturally aspirated . Forced induction is often used to increase

145-399: A fuel being present. Higher compression ratios can make gasoline (petrol) engines subject to engine knocking (also known as "detonation", "pre-ignition", or "pinging") if lower octane-rated fuel is used. This can reduce efficiency or damage the engine if knock sensors are not present to modify the ignition timing. Diesel engines use higher compression ratios than petrol engines, because

174-420: A supercharger - in order to function. A reduced density of intake air is caused by the loss of atmospheric density seen with elevated altitudes. Therefore, an early use of forced induction was in aircraft engines. At 18,000 feet (5,500 m), the air is at half the pressure of sea level, which means that an engine without forced induction would produce less than half the power at this altitude. Forced induction

203-457: A supercharger for increased power and is coupled with a 15 kW (20 hp) electric motor, Dual Clutch System, and lithium-ion battery for increased fuel efficiency . The engine has a compression ratio of 9.1:1 (10.0:1 in 2014 Infiniti QX70) and produces a combined 250 hp (186 kW; 253 PS) at 5600 rpm and 243 lb⋅ft (329 N⋅m) at 3600 rpm. Vehicle applications: Compression ratio The compression ratio

232-556: A variable compression ratio was introduced in 2019. Variable compression ratio is a technology to adjust the compression ratio of an internal combustion engine while the engine is in operation. This is done to increase fuel efficiency while under varying loads. Variable compression engines allow the volume above the piston at top dead centre to be changed. Higher loads require lower ratios to increase power, while lower loads need higher ratios to increase efficiency, i.e. to lower fuel consumption. For automotive use this needs to be done as

261-492: Is 6100 rpm. Altimas that are PZEV compliant create 170 hp (127 kW; 172 PS) and 175 lb⋅ft (237 N⋅m) of torque. [2] In the 2005+ Nissan Frontier the QR25DE generates 152 hp (113 kW; 154 PS) and 171 lb⋅ft (232 N⋅m) of torque. [3] The revised QR25DE found in the 2007+ Sentra, Altima, Rogue , etc. has a number of improvements over the older QR25DE. These include: The QR25DD

290-518: Is 89 mm × 100 mm (3.50 in × 3.94 in) and a compression ratio ranging from 9.5:1 to 10.5:1 depending on the vehicle. Output is rated 175 hp (130 kW; 177 PS) at 6000 rpm with 244 N⋅m (180 lb⋅ft) of torque at 4000 rpm in the Altima 2.5 and Sentra SE-R models. The Sentra SE-R Spec V originally claimed 180 hp, but this was adjusted downward to 175 once production started in late 2001. The redline

319-464: Is a polytropic value for the ratio of specific heats for the combustion gases at the temperatures present (this compensates for the temperature rise caused by compression, as well as heat lost to the cylinder) Under ideal (adiabatic) conditions, the ratio of specific heats would be 1.4, but a lower value, generally between 1.2 and 1.3 is used, since the amount of heat lost will vary among engines based on design, size and materials used. For example, if

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348-480: Is at the top of its stroke . The dynamic compression ratio is a more advanced calculation which also takes into account gases entering and exiting the cylinder during the compression phase. A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air–fuel mixture due to its higher thermal efficiency . This occurs because internal combustion engines are heat engines , and higher compression ratios permit

377-628: Is higher with more conservative intake camshaft timing (i.e. soon after BDC), and lower with more radical intake camshaft timing (i.e. later after BDC). Regardless, the dynamic compression ratio is always lower than the static compression ratio. Absolute cylinder pressure is used to calculate the dynamic compression ratio, using the following formula: P cylinder = P atmospheric × CR γ {\displaystyle P_{\text{cylinder}}=P_{\text{atmospheric}}\times {\text{CR}}^{\gamma }} where γ {\displaystyle \gamma }

406-522: Is similar to the QR20DE but features NEO direct injection to improve fuel economy and to reduce emissions. [1] It produces 150 PS (110 kW; 148 hp) at 6000 rpm and 200 N⋅m (148 lb⋅ft) at 4400 rpm. Vehicle applications: The QR25DE is a 2.5 L (2,488 cc) variant built with cast steel connecting rods, a steel timing chain, counter-rotating balance shafts , and an aluminum intake manifold. The engine bore and stroke

435-400: Is similar to the QR25DE but increases the compression ratio to 10.5:1 and includes direct injection. This engine is also the first QR to use DLC coating on the valve lifter buckets for reduced friction. It produces 125 kW (170 PS; 168 hp) at 5600 rpm and 245 N⋅m (181 lb⋅ft) at 4000 rpm. Vehicle applications: The QR25DER is similar to the QR25DE but has

464-407: Is the ratio between the volume of the cylinder and combustion chamber in an internal combustion engine at their maximum and minimum values. A fundamental specification for such engines, it can be measured in two different ways. The simpler way is the static compression ratio : the ratio of the volume of the cylinder when the piston is at the bottom of its stroke to that volume when the piston

493-484: Is used to artificially increase the density of the intake air, in order to reduce the loss of power at higher altitudes. Systems that use a turbocharger to maintain an engine's sea-level power output are called "turbo-normalized" systems. Generally, a turbo-normalized system attempts to maintain a manifold pressure of 29.5 inHg (100 kPa). The most commonly used forced-induction devices are turbochargers and superchargers. A turbocharger drives its compressor using

522-661: The Ferguson TE20 tractor had a compression ratio of 4.5:1 for operation on tractor vaporising oil with an octane rating between 55 and 70. Motorsport engines often run on high-octane petrol and can therefore use higher compression ratios. For example, motorcycle racing engines can use compression ratios as high as 14.7:1, and it is common to find motorcycles with compression ratios above 12.0:1 designed for 95 or higher octane fuel. Ethanol and methanol can take significantly higher compression ratios than gasoline. Racing engines burning methanol and ethanol fuel often have

551-474: The case of high-performance engines. Four-stroke diesel engines are well suited to forced induction, since the lack of fuel in the intake air means that higher compression ratios can be used without a risk of pre-ignition. Therefore, the use of turbochargers on diesel engines is relatively commonplace. Two-stroke diesel engines have a significantly different operating principle to two-strokes petrol engines, and require some form of forced induction - generally

580-420: The complex shape of V c {\displaystyle V_{c}} it is usually measured directly. This is often done by filling the cylinder with liquid and then measuring the volume of the used liquid. Most engines use a fixed compression ratio, however a variable compression ratio engine is able to adjust the compression ratio while the engine is in operation. The first production engine with

609-561: The density of air increases with pressure, this allows a greater mass of air to enter the combustion chamber. Theoretically, the vapour power cycle analysis of the second law of thermodynamics would suggest that increasing the mean effective pressure within the combustion chamber would also increase the engine's thermal efficiency . However, considerations (such as cooling the combustion chamber, preventing engine knock and limiting NOx exhaust emissions) can mean that forced induction engines are not always more fuel efficient, particularly in

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638-432: The engine is running in response to the load and driving demands. The 2019 Infiniti QX50 is the first commercially available car that uses a variable compression ratio engine. The static compression ratio discussed above — calculated solely based on the cylinder and combustion chamber volumes — does not take into account any gases entering or exiting the cylinder during the compression phase. In most automotive engines,

667-430: The first such commercial engine from 2013, used adaptive fuel injectors among other techniques to ease cold start. The compression ratio may be higher in engines running exclusively on liquefied petroleum gas (LPG or "propane autogas") or compressed natural gas , due to the higher octane rating of these fuels. Kerosene engines typically use a compression ratio of 6.5 or lower. The petrol-paraffin engine version of

696-473: The formula C R = V d + V c V c {\displaystyle \mathrm {CR} ={\frac {V_{d}+V_{c}}{V_{c}}}} where V d {\displaystyle V_{d}} can be estimated by the cylinder volume formula: V d = π 4 b 2 s {\displaystyle V_{d}={\tfrac {\pi }{4}}b^{2}s} where Because of

725-463: The intake valve closure (which seals the cylinder) takes place during the compression phase (i.e. after bottom dead centre , BDC), which can cause some of the gases to be pushed back out through the intake valve. On the other hand, intake port tuning and scavenging can cause a greater amount of gas to be trapped in the cylinder than the static volume would suggest. The dynamic compression ratio accounts for these factors. The dynamic compression ratio

754-450: The lack of a spark plug means that the compression ratio must increase the temperature of the air in the cylinder sufficiently to ignite the diesel using compression ignition . Compression ratios are often between 14:1 and 23:1 for direct injection diesel engines, and between 18:1 and 23:1 for indirect injection diesel engines. At the lower end of 14:1, NOx emissions are reduced at a cost of more difficult cold-start. Mazda's Skyactiv-D ,

783-404: The power output of an engine. This is achieved by compressing the intake air, to increase the mass of the air-fuel mixture present within the combustion chamber . A naturally aspirated engine is limited to a maximum intake air pressure equal to its surrounding atmosphere ; however a forced induction engine produces "boost", whereby the air pressure is higher than the surrounding atmosphere. Since

812-423: The same combustion temperature to be reached with less fuel, while giving a longer expansion cycle, creating more mechanical power output and lowering the exhaust temperature. In petrol (gasoline) engines used in passenger cars for the past 20 years, compression ratios have typically been between 8:1 and 12:1. Several production engines have used higher compression ratios, including: When forced induction (e.g.

841-424: The static compression ratio is 10:1, and the dynamic compression ratio is 7.5:1, a useful value for cylinder pressure would be 7.5 × atmospheric pressure, or 13.7  bar (relative to atmospheric pressure). The two corrections for dynamic compression ratio affect cylinder pressure in opposite directions, but not in equal strength. An engine with high static compression ratio and late intake valve closure will have

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