The Evolution of Spark-Ignited Gasoline Engines

Technically speaking the ICE technology is rooted in the first commercial gas turbine patented by English inventor John Barber in 1791. It was followed three years later by a gas engine born from the hands of Thomas Mead and, that same year, by the first engine to use liquid fuel, the brainchild of one Robert Street.

History credits Nicolaus Otto with inventing the four-stroke cycle engine. Working on a compressed charge, it was assembled in 1876 with help from two men who would define the automotive industry: Gottlieb Daimler and Wilhelm Maybach.

Believe it or not, the engines we use today, although much more advanced than what was available back then, share the same operating principles with its ancestors. In a nutshell, that means introducing liquid fuel into the combustion chamber, accompanied by just the right amount of air, and then ignite the mixture with help from a spark.

What is now different than it used to is the way the fuel-air mixture is delivered into the cylinders and ignited. The evolution of this system came not only from the need to make engines better but also less harmful to the environment.

For the better part of their existence ICE units were fed the magical mixture by means of carburetors. That would be pieces of hardware installed on top of the engine block, beneath the air filter. Using a combination of vacuum power and cable control, it mixed fuel with air and sent it to the cylinders where it could safely explode.

The solution worked wonders and stayed in use from the early days of the automobile at the start of the last century until the early 1990s when it started being replaced by injectors. Carburetors still are present on our roads today in classic cars, and on top of that they still are the fuel delivery method of choice for custom car builders.

But carburetors are not the most efficient way of delivering fuel to an engine. They came with low fuel efficiency, created lag due to slow throttle response, and for those looking for performance they required constant adjustments to the air-fuel mixture. And it is is in part because of that that the injection system was invented.

The tech relies on injectors that mix air with fuel to, well, inject the mixture into the combustion chamber. The proportions of fuel and air to be used are in our time calculated by computers, so cars get better atomization, a cleaner combustion, and better throttle response.

Mechanical Fuel Injection (MFI)

Technically speaking fuel injection in automobiles dates back to the early 1950s, despite the fact it was first used in the 1910s in a two-stroke aircraft engine created by Otto Mader. It was slow to catch on, though, because such a system is costlier than carburetors, and it required costly tools to fine-tune the system and perform repairs. So it wasn't until some four decades later that injection begun to be adopted en masse.

The early fuel injection systems were of the mechanical variety (MFI). Initially intended for use in fighter planes during the Second World War, it slowly made its way into cars – granted, it was reserved for the more expensive of the bunch, at least at first.

Mechanical fuel injection works by operating a throttle-controlled air valve and a fuel pump. Unlike the carburetors that preceded it, the MFI reliably provided a precise quantity of fuel and air for every combustion cycle.

These systems were perfected over the years and ended up being manufactured well into the late 1980s. They didn’t last for long, though, as they did come with a series of drawbacks, including the fact they needed occasional adjustments.

Electronic Fuel Injection (EFI)

As said, current cars use a fuel injection system rather than a carbureted one. It’s not the mechanical fuel injection we discussed earlier, but of the electronic variety.

What the electronic part of the system is supposed to mean is that now injection is controlled by an engine control unit, one of the many computers that go in today’s cars. Its arrival marked the next real advancement in reducing emissions of gasoline engines (but also diesel ones) because it brought about better control over the amount of air-fuel mixture that went into the combustion chamber.

EFI first arrived into the world as single-point injection systems, meaning there was only one injector in the throttle body. Pretty soon, though, multi-point injection started being adopted, but that proved out to be less efficient than hoped.

As opposed to the mechanical fuel injection systems, EFI relies on a variety of sensors that allow it to operate with improved precision. It is controlled by dedicated computers that allow a stoichiometric mixture of air and fuel to be fed into the engine at any speed and moment of operation.

One of the crucial sensors for the operation of the EFI is the so-called lambda one. Technically an oxygen sensor, it is installed in the exhaust gallery. Its sole purpose for being is to determine the efficiency of the combustion cycle and of the pollution-reducing devices that are now norm, like say catalytic converters.

Two or more oxygen sensors are also used, placed in a stream on the exhaust gallery, usually before and after the catalytic converter.

Using data from these sensors, computers continuously adjust ignition timing and injection so that they match the parameters set by the factory, in an effort to ensure that the operation of the gasoline engine fully complies with emission regulations.

Gasoline Direct Injection (GDI)

While not a recent invention, direct-injected gasoline engines have been on the rise over the last few years. As opposed to single-point and multi-point systems, direct injection delivers the fuel mixture at a higher pressure and directly into the combustion chamber.

As you know, classical fuel injection sends lower-pressure fuel in the intake gallery. Direct-injection gasoline engines were inspired by diesel powerplants and had the injectors deliver the fuel directly into the combustion chamber. Thanks to ingenious engineering, these injectors are capable of spraying an even smaller amount of gas in the combustion chamber, and can even do this to form a particular pattern that will ignite optimally.

Doing things this way can increasese the efficiency of the engine, but also its output.

Exhaust Gas Recirculation Valve (EGR)

Fitting the new fuel injection system on engines was not the only improvement made to the spark-ignited engines in recent times. Back in the 1970s the engineers in the U.S. came up with something called the Exhaust Gas Recirculation Valve (EGR).

The system's main goal was to reduce harmful engine emissions while improving efficiency. General Motors was the first to try this out, and it found that the EGR did all that by reusing up to 35 percent of the exhaust gases from fuel burn.

The working principle of the EGR is pretty simple. Some of the exhaust gases were injected back into the combustion chamber in a bid to tamper with the operating temperature.

This resulted in the reduction of oxygen levels and, in a nutshell, the engines reached operating temperature faster, while the opposite effect, a reduced peak temperature, was achieved in the cylinders. As a result, pre-ignitions and detonations were prevented, making the engine run smoother.

However, the early EGR systems were crude in design and operation and impacted the engine's operation. To improve them, carmakers started controlling these systems to allow them to deliver improved startup and idling. Disabling the system enhanced performance on high loads.

Most modern cars still feature an EGR system, while some engines have managed to go without it through various solutions. EGR can be used in both diesel and gasoline engines, and in some cases, it can also be applied to hydrogen powerplants.

Electronic Ignition Systems

In an internal combustion engine, the ignition system initiates combustion. In the case of the gasoline engines we're discussing now, that is through spark ignition, which means exactly that: a spark ignites the air-fuel mixture, getting the pistons going (in diesel engines the same is achieved using compression).

In early gasoline vehicles, ignition was done through magneto or induction coil systems. The former relied on a magneto and a transformer to generate high-voltage pulses for the spark plugs, while the latter relied on the car's battery and the sending of current through a coil, which generated a series of sparks during firing.

It wasn't until the electronic ignition system was introduced that gasoline engines really reached their peak potential. First used in the late 1940s, the technology evolved to such a degree that it is now something akin to art.

Using a series of sensors that replaced the vacuum-operated and centrifugal timing advance mechanisms of traditional distributors, electronic ignition timely generated the spark needed for the engine to start running.

Electronic ignition was first deployed on cars that used carburetors to improve their efficiency. Rapidly, it became the norm for gasoline engines.

Lean Burn

When talking about a lean burn in a combustion engine people mean making it run in such a way as to burn the fuel with an excess of air inside the combustion chamber. This abundance of oxygen, crucial for any burn to sustain itself, involved using a different air/fuel ratio, several times higher than the stoichiometric 14.64:1 considered the optimum one for the Otto cycle engine.

The concept of a lean burn came to be in the 1970s and it was rapidly seen as a good way to cut back on throttling losses that usually occur due to the design of the throttle body. A great side effect of this was that fuel economy got better.

Carmakers like Chrysler, Honda, Nissan, Mitsubishi, and Toyota tried out the idea, but it didn't really catch on. Responsible for that are a series of drawbacks, including the need to deploy complicated catalytic converters. The idea kind of died out at about the same time fuel injection started becoming norm, in the 1990s.

Catalytic Converter

When it comes to emissions, the operation of a vehicle is kept in check by a variety of technologies, and few of them are as important in our day and time as the catalytic converter. It's a piece of technology that operates alongside the electronic fuel injection to help the car achieve lower emission levels.

The technology dates back to the 1950s, and it works now in pretty much the same way it did before. The way the converter cuts emissions is by creating an oxidation reaction inside of its shell with the aid of the rare metals it contains. This reduces the amount of nitrogen oxides by effectively splitting the molecules into nitrogen and oxygen.

Other Combustion Cycle Engines

The Otto combustion cycle is not the only way gasoline engine can operate. Back in 1882, British engineer James Atkinson developed the combustion cycle that still wears his name. It was not as popular as the Otto cycle because of the reduced power density it provided, but it is a solution that, modern hybrids use thanks to its improved overall efficiency.

To compensate for the reduced power density of the Atkinson cycle, some engines have been developed to run with the aid of a mechanical supercharger. These are called Miller-cycle engines. Yet, unlike the Otto engines using the Atkinson cycle, these are not widespread.

Some automakers have developed spark-ignited engines that work in Atkinson cycle at low loads, and then turn to the Otto cycle to provide a high output. Mazda does this with its 2.0-liter Skyactiv-G units, and Toyota uses a similar concept on the Lexus NX200 t's engine, among others.

What the future holds

The future may belong to the electric car, but that doesn’t mean ICE cars, including the ones powered by gasoline engines, will disappear. Quite the contrary, we expect them to keep evolving.

We expect future gasoline engines to feature improved spark plugs, like the laser-operated hardware Mazda is making for its rotary engines. Furthermore, the throttle body might be eliminated because of the pumping losses it generates (BMW already does this on its Valvetronic engines), while the combustion cycle could be further improved through fully adjustable timing.

Currently, variable valve timing is the norm in the auto industry along with direct injection, but Koenigsegg has already developed a cam-less engine with fully variable timing to improve power and efficiency.