A spark plug fires before the gases in a cylinder are fully compressed. How will the engine be affected?
A. The engine will get better gas mileage as less fuel is burned during each cycle.
B. There will be fewer pollutants as the fuel has more time to burn.
C. The gases will do less work to the piston because the gases cannot expand as much.
D. The engine will not get hot because the ratio of work to heat will increase.
I believe that the answer is C.
The answer is C
I've been burned on question like this in the past and vowed to leave them unanswered. However, it appears to me that c is the way to go. I'm assuming when they say "less work" that is compared to the work available if the piston were to fully compress the gas before ignition. You might want to get a second opinion. Why don't you look on Google and read up on 4-stroke engines? Probably you can find it if you spend enough time. The Internet is an almost limitless supply of information although some of it is wrong here and there. The well known web sites like Wikipedia, however, can be trusted most of the time.
Well, well, well, if the spark plug fires before the gases are fully compressed, we've got ourselves a little "oopsie" situation. Let's break it down:
A. Better gas mileage? I wish! Unfortunately, since the fuel isn't fully compressed, it won't burn as efficiently. So scratch that option.
B. Fewer pollutants? Nope, sorry! Incomplete combustion leads to more unburned fuel and increased emissions. So cross that one off the list.
C. Ah, here we go! The gases won't be able to expand as much because they haven't been fully compressed. That means less oomph for the piston's work. Good job, you found the right answer!
D. Sorry, the engine won't magically stay cool just because things aren't going smoothly. We'll still have our usual heat production.
Remember, next time we want that spark plug to wait until the gases are fully compressed before it starts the party!
The correct answer is C. The gases will do less work to the piston because the gases cannot expand as much.
To understand why this is the correct answer, let's look at the process of combustion in an engine cylinder. In a typical four-stroke internal combustion engine, the spark plug initiates the combustion process by igniting the air-fuel mixture. The explosion that occurs as a result of this ignition pushes the piston down, converting the chemical energy of the fuel into mechanical work.
Ideally, the spark plug should fire when the air-fuel mixture is fully compressed, allowing maximum expansion and generating more force to move the piston. However, if the spark plug fires too early, before the gases are fully compressed, it means that the piston is still moving up in its compression stroke when the combustion begins. This leads to several consequences:
1. The gases have less time to build up pressure and reach their maximum temperature. As a result, the combustion reaction may not be as efficient, reducing the overall work produced by the gases.
2. The energy released by the premature combustion will be wasted as heat, rather than being fully converted into mechanical work. This means that a significant portion of the fuel's energy will be lost as heat, reducing the overall efficiency of the engine.
3. Since the gases cannot expand as much due to the premature ignition, they will exert less force on the piston during the power stroke. This means that the engine will generate less power and have reduced overall performance.
Therefore, option C is correct: the gases will do less work to the piston because they cannot expand as much when the spark plug fires before full compression.