Yes, the heat plays an important role but without the increased oxygen the heat developed by the combustion would be less, if combustion could still be sustained a lower oxygen levels. ----- Original Message ----- From: "Michael Rigby-Jones" To: "Microcontroller discussion list - Public." Sent: Thursday, June 28, 2007 6:42 AM Subject: RE: [EE] Simple fuel-saver, so they say > > >>-----Original Message----- >>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] >>On Behalf Of Rich >>Sent: 28 June 2007 06:35 >>To: Microcontroller discussion list - Public. >>Subject: Re: [EE] Simple fuel-saver, so they say >> >> >> The expanding forces against the side walls of the cylinder do not >>contribute to the force on the piston head and so contribute to the >>inefficiency. > > I'm not sure this can be true. The very fact that the cylinder and > cylinder head are present is what creates the pressure in the first place. > Exterting pressure on a static body performs no work. What does reduce > efficiency is the cylinder, head and piston absorbing heat from the > burning fuel/air mixture, which is why ceramic coatings have been > developed to try to reduce this (for piston and head at least). > > >>In diesel engines the compression ratio is much >>higher and it >>is so oxygen rich that a spark is not required to initiate the >>burn. > > The reason it does not need a spark is because the heat created during > compression is used instead. This heat would also readily ignite a > stoichiometric gasoline/air mixture, but the resulting burn would not be > controlled, e.g. detonation. > > >> The reason diesel can >>tolerate >>higher oxygen ratios is because there is less BTU per unit >>volume than for >>gasoline, of whatever octane. > > Diesel actually has a higher energy content than gasoline. Also note that > octane rating is not an indicator of energy content of gasoline! In fact > very often the high octane fuels will have slightly lower energy density, > because the additives required to increase the octane rating displace some > fuel (e.g. what used to be tetra-ethyl lead many years ago). High octane > simply means that the fuel has improved resistance to detonation, so a > higher compression ratio can be used to extract more energy from the fuel. > > The reason that very weak (i.e. excess oxygen) mixtures can be ignited in > a diesel is because they do not rely on a small spark located at one point > in the combustion chamber, instead the fuel is injected into the > compressed and heated air and starts burning immediately. In a gasoline > engine, the mixture has to have enough fuel for the spark to initiate > combustion. This is why stratified charge engines have been developed, > this creates a small fuel rich mixture around the spark plug, surrounded > by a larger volume of weak mixture. Once the rich mixture is ignited, the > flame front will happily propagate through the weaker regions. The GDI > engines that e.g. Mitsubishi have developed rely on this. > > Note that the actual mixture ratio in a diesel varies considerably over > the engines operating range because it not throttled, i.e. the volumetric > efficiency is more or less constant, only the amount of fuel injected > varies. > > Regards > > Mike > > ======================================================================= > This e-mail is intended for the person it is addressed to only. The > information contained in it may be confidential and/or protected by > law. If you are not the intended recipient of this message, you must > not make any use of this information, or copy or show it to any > person. Please contact us immediately to tell us that you have > received this e-mail, and return the original to us. Any use, > forwarding, printing or copying of this message is strictly prohibited. > No part of this message can be considered a request for goods or > services. > ======================================================================= > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist