Nowadays, fuel prices are increasing day by day. Thanks to the incredible invention of diesel fuel, which is not only efficient but also cost-effective. The reason this engine is so affordable is that it doesn’t need a spark plug (as is the case with gasoline engines). Now, a question must come to your mind: “How do diesel engines work without spark plugs?” Well, there’s nothing magical behind it.
A small difference in operation allows this engine to ignite without needing a spark plug and run your car smoothly.
Do Diesel Engines Have Spark Plugs?
Unlike gasoline engines, diesel engines do not need spark plugs to create the ignition that ignites the intake air mixture. At the end of the compression stroke and the beginning of the power stroke, diesel fuel is injected into the diesel engine’s combustion chamber. Under the influence of the high temperature and pressure of the compressed air, self-ignition occurs. Simply put, diesel engines have a high compression ratio, so they don’t need an ignition device (spark plug). However, in fact, self-detonation still occurs in both gasoline and diesel engines at a low compression ratio.
Furthermore, some diesel engines are equipped with an additional glow plug. In winter, the compressed air does not create sufficient temperature and pressure, which can cause self-ignition upon diesel injection. The reason is that the engine’s combustion chamber is too cold. At that point, the glow plug has the effect of heating the combustion chamber before starting the engine.
Thus, there is no ignition step in diesel engines. In conclusion, diesel must have a high flash point and a low auto-ignition temperature. The definition of a fuel’s “flash point” is the lowest point at which it can mix with air to form a flammable mixture. The “high flash point” of diesel fuel means it doesn’t burn as easily as gasoline, which is a safe condition. A flash point that is too low will also damage the engine because the fuel continues to combust and the fuel burns before the explosion.
As we know, the ignition system is an essential component of a vehicle (gasoline engine). If the ignition system doesn’t work, your car won’t start, and that’s why the ignition system is so important. On the other hand, in diesel engines, we don’t see the presence of this system. Let’s find out why diesel engines don’t have an ignition system (spark plugs).
Main Reason Why Diesel Engines Work Without Spark Plugs
A spark plug is used in gasoline engines and vice versa in diesel engines which do not use them. Gasoline and diesel have different properties, one of which is auto-ignition (thanks to pressure and temperature). Diesel has a low auto-ignition temperature. Auto-ignition temperature means the fuel starts to burn automatically at a specified temperature. Due to its low auto-ignition temperature, diesel can easily ignite. To better understand the reasons behind this question, let’s read these reasons below to find out why diesel engines produce sparks without requiring a spark plug at all, right now!
1. Low Volatility
In diesel engines, air and fuel injection occur at different stages. The compression ratio can range from 14:1 to 25:1. The idea behind the diesel engine design is to have higher compression ratios. The less volatile nature of diesel, therefore, tends to have a low auto-ignition temperature.
However, another reason is their power cycle, according to which the higher compression ratio (mentioned above) is not possible to achieve with gasoline, as the risks of self-ignition or engine knocking are high.
But, to include such a high pressure ratio, the cost of the engine will increase, so to keep it commercial, manufacturers found a solution to increase the temperature of the fuel as well as the combustion chamber through glow plugs (drying plugs). This also offers usage comfort, as during low starting temperatures or in cold weather, the glow plug will also provide heat to the cylinder and combustion chamber. Diesel has low volatility, so it cannot be like a gasoline and air mixture to be ignited by a spark plug.
2. Auto-Ignition Temperature
Due to diesel’s auto-ignition properties being lower than those of gasoline and petrol, the temperature generated by compressing air during the compression stroke is sufficient to ignite the atomized diesel fuel. The temperature can be 1000°F or more, which is enough to ignite the fuel. This clearly shows that the diesel engine is an improvement over gasoline engines, as in these engines, only air is compressed during the compression stroke, making them capable of operating even at a much higher temperature ratio.
In contrast, gasoline engines have an inability to operate at higher temperature ratios; even if they operate at a high temperature, the air-fuel mixture can ignite. This can lead to knocking and detonation, and for that, you might also need some maintenance tips. That’s why the lower auto-ignition capability makes the diesel engine an improved version of the SI (gasoline) engine.
So, that’s how diesel engines work efficiently and quickly without spark plugs.
3. Negligent Use of Spark Plugs
Atmospheric air is trapped in the diesel engine’s cylinder, which is then compressed at high pressure. This process ultimately increases the temperature, and when the engine goes into action at the end of the compression stroke, ignition occurs and the fuel burns. This naturally eliminates the need for a spark plug to ignite the engine.
That’s why the diesel engine does not require a spark plug. Furthermore, these engines have overcome the drawbacks of previous engines, such as noise and spark plug maintenance. Therefore, diesel engines work without spark plugs to save fuel, time, and money simultaneously.