The Difference Between A Spark Plug and A Glow Plug!

All right guys so in this hand I have a glow plug and in this hand I have a spark plug. Why am I showing you a glow plug and a spark plug? Because over the years I have gotten tired of the answer to the question of why diesel engines don't use a spark plug being that they use a glow plug instead. So this needs to be out there people need to understand they're going to be working on diesels that these are two entirely different entities that do two entirely different things. All right so let's start with the spark plug. This spark plug does the heat part of the ignition process. So remember to make fire to make combustion occur you need three things right. You need a fuel source, you need oxygen, and you need heat. All right so in a gasoline engine obviously the gasoline is the fuel source the oxygen is what's coming into the cylinder on the intake stroke along with the fuel. So you got those two in there and then this guy is what provides the heat component. So without the spark plug no kaboom right no power stroke because the spark that occurs right here is what ignites that fuel air mixture in a gasoline engine and causes the combustion process to begin right. So that's it this is supplying the heat for combustion. On a diesel engine right we have our three things that we need the heat the compression or I'm sorry the heat the fuel and the man I'm running out of words here oxygen right so heat oxygen and the fuel. So on the intake stroke of a diesel only air is entering the cylinder the air gets compressed creates its own heat and then it ignites the fuel when it's delivered by the injector. So that's why we don't need one of these right the diesel air gets hot enough to ignite the fuel on its own without the aid of a spark plug igniting it right. So what does this guy do well here's where it gets interesting it does not take the place of a spark plug these two things operate off of very different principles. This is required for ignition the engine will not run without it. This is a starting aid it is used to preheat the combustion chamber in cold ambient temperatures so that the compression of the air can still make it hot enough to ignite the fuel. Once the engine reaches a certain temperature this thing goes off it stays off and you don't need it anymore and the engine will stay running. If you shut this guy off the engine stops right so starting aid glow plug ignition source spark plug. I hope that clears up the difference between the two if you have any questions about that that go deeper please put them in the comments I'll be more than happy to explain them but remember starting aid only used to start a truck in cold temperatures and eventually shuts off and you don't need it for the engine to run. Ignition source you need it for the engine to run right two very different things so next time someone asks you why a diesel engine doesn't use spark plugs it's not because it uses glow plugs instead it's a completely different thing. The reason it doesn't need a spark plug is because it uses compression ignition instead of spark ignition. All right so thank you for watching this I hope this cleared up some misconceptions that might be out there and again thank you for watching any questions put them in the comments I'll be more than happy to answer and thanks for coming on to Charlie's Garage. Bye!