You see this term with more and more cars these days: direct injection. What is it, how does it work, and why should you want it? Let’s dive into it.
With the launch of the Proton X50 on the horizon, it isn’t surprising that the compact SUV is on everyone’s mind. From the uncle at your local kopitiam, to your colleagues, to even the nagging auntie in the family WhatsApp group – everyone has an opinion on Proton’s next big hit. But one of the curious things is that there is a singular engine variant across the range – a turbocharged 1.5-litre 3-cylinder petrol heart – but offered with or without direct injection.
The direct-injection engine variant comes in the Flagship model that sits at the top of the range, and it churns out a healthy 174 PS and 255 Nm of torque – impressive figures for an engine of this size. As opposed to this, the port injection engine variant makes 150 PS and 226 Nm of torque. Let’s go through how it all works, and why it matters.
The main principles of how an engine operates have not changed since the dawn of the internal combustion engine, but efficiency and cleanliness has increased dramatically over the years and decades. A lot of this is down to how fuel gets from outside the engine to inside the engine – which we will call fuel delivery.
Up until the 1980s, the majority of road cars used something called a carburettor. This mechanical device sat on the intake manifold – basically how air gets into the engine – and when you press the accelerator pedal, it would dump fuel into your engine like you were turning on a tap. This method of fuel delivery worked, but it was crude in many ways and very sensitive to things like weather and temperature. It was also extremely inefficient.
When electronic fuel injection (EFI) came around, it made a massive difference to how smoothly, reliably, and efficiently engines ran. Most engines would have a dedicated fuel injector for each cylinder, which would spray fuel directly into the individual intake for each cylinder. With computer controlled fuel injection, engineers could program it to spray just enough fuel to keep the engine running happily, regardless of engine speed.
But as much as a difference this made, there was still a ways to go when it came to fuel delivery. This is because the way these EFI systems worked is they would spray fuel on the walls of the intake tract and a closed valve – once the valve opened like a bouncer opening the doors to a club, the air being sucked into the engine would carry most of the fuel with it. This presented a problem of having small amounts of wasted fuel still sitting in the intake tract, as well as trying to figure out how to atomize that fuel to make it burn properly in the cylinder.
When an engine burns the fuel inside of the cylinder, how well it burns and how cleanly it burns depends on how well mixed the air and fuel is inside the cylinder – like how you have to stir your kopi panas to make sure the condensed milk properly mixes with the hot coffee. To achieve a good mix, atomizing the fuel into tiny tiny droplets greatly helps – and unfortunately, EFI still had its limits.
That’s where direct injection came in. With the introduction of direct injection, we called traditional EFI systems “port injection” for contrast, as they sprayed fuel at the intake ports. Direct injection engines have the fuel injectors spraying right into the cylinder, at extremely high pressures and at any point in the combustion cycle. This means that an engine could spray EXACTLY the right amount of fuel needed for combustion, with little to no wastage or loss.
The fuel that is sprayed in is also atomized extremely well because of the design of these injectors, which also leads to a much better, cleaner burn. For reasons that are a little too technical to explain here, direct injection can even run an engine on less fuel than possible with port injection because it can effectively layer how the fuel is distributed through the cylinder from the spark plug downwards, allowing for extremely lean operation.
These marvels of engineering can fire even up to 20 times in a single combustion cycle, giving total precision over the fuel delivery and setting up the engine for a clean burn. You can also achieve higher power outputs as a result because of the finer control without compromising fuel efficiency or emissions requirements.
The technology is highly complex – which is why direct injection engines usually command a premium over their port injected brethren. But the gains in efficiency and performance are definitely something you will notice – though there are a couple of drawbacks to direct injection engines that may be worth keeping in mind.
First is that the maintenance cost of direct injection fuel injectors is significantly higher than port injection units – but these items can last for over a decade as long as you keep your fuel system cleaned and serviced on time. The next issue is something that has somewhat been ironed out over the years with other cars on the market, but is something to keep in mind.
When an engine burns fuel, one of the by-products is carbon residue. As the valves open and shut, some of that carbon is picked up and stuck to them – over time this becomes a problem as the carbon builds up to the point where a valve can’t seal properly when it shuts. This wasn’t generally a problem on port injected cars because the fuel helped to wash the intake and valves of this residue, but in a direct injection engine there isn’t any fuel coming through the intake. One of the ways around this is either to run both port AND direct injection in parallel (more common than you think) or to make sure that your engine properly warms up whenever you drive it, regardless of how short your journey is.
But besides these minor foibles, there’s no reason to fear or avoid a direct injection engines – especially when you consider the benefits that the technology provides. Who doesn’t want more power, torque, and fuel economy?