How Engines Are Becoming More Fuel Efficient

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“1975. The average fuel consumption of cars. Within the. Us was around 15 miles per per gallon or 156.

Liters per 100 kilometers in. 2019 most cars. Easily achieved 30 miles per gallon. Or.

78. Litres. Per. 100.

Kilometres with. Some. Even approaching 40 miles per. Gallon.

Or. 58. Eight liters per. 100.

Kilometers. And this was without factoring in hybrid. Technologies the abrupt rise of fuel economy in the us..

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Was a direct result of a shift of fuel economy policy in 1975. This was in response to the oil price shocks of the early 1970s. This caused the transition towards smaller cars with less powerful smaller. Engines.

This trend was generally unappealing among consumers and manufacturers took note of this and started exploring technologies that would bring power and robustness back to their vehicles. While still maintaining good fuel economy to understand how this was done let s first look at how a gasoline engine works. It should be noted that the scope of this video will be limited to gasoline engines. Only though some of the principles do overlap with diesel engines an engine extracts energy from the burning of gasoline it does this by first taking in a mixture of fuel and air into a cylinder.

The total working volume of all of the cylinders in the engine is known as its displacement. It then compresses the mixture and ignites. It with a spark plug as the mixture burns it expands pushing down a piston which rotates a crankshaft the spent gases are then pushed out through the exhaust power is sent from the rotating crankshaft through the drivetrain then to the wheels now to make a vehicle more fuel efficient. We need to reduce how much energy.

It takes to move around the first step is to reduce the size of the vehicle. Less mass. Requires less energy to move with less mass to move around we can now reduce the size of the powertrain lower displacement engine with fear cylinders and a smaller drivetrain not only weigh less but also lose less energy. Getting power to the wheels.

This is called parasitic loss. And it s caused by the inherent mechanical and efficiencies of moving assemblies within the powertrain. The amount of fuel air mixture an engine can aspirate to create power is directly related to its displacement and number of cylinders by reducing engine displacement size you lower the amount powered engine can make but also the amount of fuel that consumes increasing power output. But still keeping fuel efficiency required manufacturers to get clever.

The first steps were to control the fuel usage of the engine. More accurately in order to do this we need to understand when fuel is used most and why engines and cars have five modes of operation starting idling accelerating cruising and decelerating starting idling and decelerating all use relatively tiny amounts of fuel so let s focus on acceleration and cruising these two modes are where most fuel consumption occurs from the engines point of view acceleration happens when more throttle is opened allowing it to take in more air and fuel. So that it can increase its rotational speed and power up load throttling open an engine to make more power is where its highest fuel consumption occurs cruising on the other hand occurs when the throttle is held slightly open keeping the engine speed and power output steady..

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Because the goal is usually to maintain a constant vehicle speed. We only need the minimum amount of power output to accomplish this this is where we can hone in the fuel efficiency of an engine. Most of the fuel that we use driving is caused by a combination of short bursts of acceleration and longer periods of cruising the key to balancing power and fuel economy is having strong acceleration characteristics. But efficient cruising characteristics and efficient cruising mode can offset the acceleration mode making the engine more fuel efficient overall the ideal ratio of air to gasoline is fourteen point seven to one this is known as a stoichiometric mixture and in theory.

This ratio will burn off the gasoline and extract the most amount of energy possible. But in practice this ratio becomes difficult to achieve this is because an engine. Only has a few milliseconds to vaporize and mix fuel with air before combustion as it rotates faster. The available mixing time drops further to compensate for this more fuel is added enriching.

It this allows more fuel to be burned. Without ideal mixing. Enriching is used primarily under acceleration to overcome decreasing mix times and ensure maximum power generation. But this comes with a significant penalty since we re mixing in more fuel than could ever possibly be burnt with the given amount of air unburned fuel is wasted getting the amount of enrichment.

Just right is to creating power with minimal fuel waste now on the cruising end of the equation. We don t care about power beyond the minimum needed to maintain a certain speed. This is where we can maximize fuel economy since our power requirements are constant a relatively low mixture is closer to fourteen point. Seven to one or even slightly higher used this is known as running lean since we re not utilizing all of the air and combustion running lean uses less fuel.

But can be damaging gasoline vapors by nature are very volatile within a cylinder compressed with air. It doesn t take much for the mixture to self ignite for an engine to function properly ignition must be triggered by the spark plug at a very specific time in the cycle. Uncontrolled self ignition of the mixture is called detonation and it can cause overheating and damage to the engine so combat detonation. The chamber and spark plugs are designed to prevent hot spots.

That can trigger self ignition. But even more importantly. Incoming fuel is used to cool the combustion chamber and control the rate of burning reducing the chances of detonation leaning out the mixture causes an abundance of oxygen in the combustion chamber..

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Making it prone to fast hot erratic burning increasing the risk of self ignition this limits how lean we can actually run an engine. The common factor for both power and good fuel economy is in precise fuel metering up until the 1980s. Most cars relied on carburetors to meter out fuel carburetors work by drawing in fuel. As air is ingested into the engine via the venturi effect regulated by the throttle.

The flow of air and throttle position determine how much fuel is drawn in the correct amount of fuel for the airflow is metered by flow. Restricting nozzles called jets with different jet circuits being tuned to different modes of an engines operation because of its mechanical nature carburetors lack precise control over air fuel mixture and require maintenance to keep them functioning correctly with the rise of cheaper embedded electronics and stricter efficiency and emissions requirements. Electronic fuel injection was embraced by manufacturers fuel injection works by precisely spraying pressurized field. Through computer controlled.

Injectors fuel is sprayed into the intake of the engine just before it enters. A silver. The computer that meters out fuel is known as an engine control unit or ecu. It s job is to measure.

The state of the engine using sensors and calculate the right amount of field to use for conditions. Some of the key parameters measured our engine rpm air temperature air flow into the engine throttle position and engine temperature armed with the accuracy of digital electronics and the flexibility of software manufacturers now khatoun fuel systems much closer to the ideal for both power and fuel economy because fuel injection is sprayed at higher pressures. It atomizes and mixes better with air. It can also be sprayed into the turbulent region of intake.

Flow. Enhancing mixing even further better air field. Mixing. Requires less enrichment.

Overall and improves. Both fuel economy and power on most engines. The fuel injection system..

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And the ignition system are merged. This allows the ecu to adjust the ignition point timing relative to the combustion cycle. Creating a spark earlier in the cylinder or advancing the timing can produce more power by starting combustion sooner. This allows more pressure to be produced in the combustion.

But at the risk of detonation with an ecu in control of the ignition system advance. The ignition timing. When conditions allow for it now become possible another advantage of fuel injection is that it allows for the use of feedback in the fuel delivery system during cruising the leanness of combustion is monitored by an oxygen sensor in the exhaust stream providing feedback to the ecu the ecu can uses data to trim the air fuel mixture closer to ideal boosting fuel economy this type of monitoring also allows adjustments to be made for improving the emissions reducing properties of catalytic converters sensors to detect detonation are also present on some fuel injection systems. Early sensors work by listening for the acoustical signatures of detonation on the engine block being able to detect detonation lets manufacturers tune engines even leaner for better fuel economy.

If detonation is detected the mixture can be enriched and the ignition timing adjusted to reduce detonation by the early 1990s fuel injection became the standard of the automotive industry manufacturers would soon start looking at other parts of the engine as well as further evolving fuel injection to meet the diverging requirements of more power. But better fuel economy in the second video on this topic. We ll take a look at some of these technologies such as variable valve timing. Cam.

Phasing. High compression. Engine. Design and small engine.

Turbo. Charging. We. ll also take a look at how manufacturers have evolved fuel injection by making use of some advanced techniques such as direct injection and ionic ignition sensing.

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