Engines using indirect injection generally have lower levels of knock than direct injection engine, due to the greater dispersal of oxygen in the combustion chamber and lower injection pressures providing a more complete mixing of fuel and air.ĭiesels actually do not suffer exactly the same "knock" as gasoline engines since the cause is known to be only the very fast rate of pressure rise, not unstable combustion. This sudden increase in pressure and temperature causes the distinctive diesel 'knock' or 'clatter', some of which must be allowed for in the engine design.Ĭareful design of the injector pump, fuel injector, combustion chamber, piston crown and cylinder head can reduce knocking greatly, and modern engines using electronic common rail injection have very low levels of knock. By this time there is already a quantity of fuel in the combustion chamber which will ignite first in areas of greater oxygen density prior to the combustion of the complete charge. There is a short lag between the fuel being injected and combustion starting. Knocking is more or less unavoidable in diesel engines, where fuel is injected into highly compressed air towards the end of the compression stroke. It supports what you said (diesels always knock) but then goes on to say they don't: Like petrol has a RON, diesel has the cetane number:Īlso, you may be interested in this little bit from the wiki concerning engine knocking. Well, almost immediately - there is a delay and this can affect the running characteristics. The fuel mixing with the extremely hot air immediately ignites. That's where you get the RON/MON ratings for different fuels - it's a measure of how well they resist knocking.ĭiesels, on the other hand can't knock like a petrol does, as the air is compressed before you add the fuel. The wrong fuel or leaning out can cause the mixture to ignite before the spark initiates it at the right time. Knock in a petrol occurs because you are compressing a mixture of fuel and air. We make our world significant by the courage of our questions and by the depth of our answers. For more open-ended questions, try /r/AskScienceDiscussion | Sign up to be a panelist!. Looking for flair? Sign up to be a panelist!.Neuroscience, Neurology, Neurochemistry, Cognitive NeuroscienceĪskScience AMA Series: Crawford Lake, Anthropocene EraĪsk Anything Wednesday - Engineering, Mathematics, Computer scienceĪsk Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, PsychologyĪsk Anything Wednesday - Economics, Political Science, Linguistics, AnthropologyĪsk Anything Wednesday - Physics, Astronomy, Earth and Planetary Science Medicine, Oncology, Dentistry, Physiology, Epidemiology, Infectious Disease, Pharmacy, Human Body Psychology, Cognitive Psychology, Developmental Psychology, Abnormal, Social Psychology Social Science, Political Science, Economics, Archaeology, Anthropology, Linguisticsīiology, Evolution, Morphology, Ecology, Synthetic Biology, Microbiology, Cellular Biology, Molecular Biology, Paleontology Mechanical Engineering, Electrical Engineering, Structural Engineering, Computer Engineering, Aerospace EngineeringĬhemistry, Organic Chemistry, Polymers, Biochemistry Mathematics, Statistics, Number Theory, Calculus, AlgebraĪstronomy, Astrophysics, Cosmology, Planetary FormationĬomputing, Artificial Intelligence, Machine Learning, ComputabilityĮarth Science, Atmospheric Science, Oceanography, Geology Theoretical Physics, Experimental Physics, High-energy Physics, Solid-State Physics, Fluid Dynamics, Relativity, Quantum Physics, Plasma Physics /r/AskScienceDiscussion: For open-ended and hypothetical questions.FAQ: In-depth answers to many popular questions.Weekly Features: Archives of AskAnything Wednesday, FAQ Fridays, and more!.Be civil: Remember the human and follow Reddiquette.Report comments that do not meet our guidelines, including medical advice.Downvote anecdotes, speculation, and jokes.Upvote on-topic answers supported by reputable sources and scientific research.Answer questions with accurate, in-depth explanations, including peer-reviewed sources where possible.Please read our guidelines and FAQ before posting
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |