Investigations on lean combustion in a petrol engine

Abstract

Lean operation of spark ignition (SI) automotive engines offers attractive performance incentives. Lowered combustion temperatures inhibit NOx, pollutant formation while reduced manifold throttling minimizes pumping losses, leading to higher efficiency. These benefits are offset by the reduced combustion speed of lean mixtures, which can lead to high cycle-to-cycle variation and unacceptable engine behavior characteristics. Hydrogen-enhancement can suppress the undesirable consequences of lean operation by accelerating the combustion process, thereby extending the quotlean limit.quot Hydrogen can be produced onboard the vehicle with a plasmatron fuel reformer device. newlineIn this work, research efforts made in three different phases with the objective of improving the fuel economy of and reducing exhaust emissions from conventional, carbureted, two-stroke spark ignition (SI) engines, which are widely employed in two-wheel transportation in India. A review concerning the existing two-stroke engine technology for this application is included. In the first phase, a new scavenging system was developed and tested to reduce the loss of fresh charge through the exhaust port. In the second phase, the following measures are carried out to improve the combustion process: (i) using an in-cylinder catalyst, such as copper, chromium, and nickel, in the form of coating; (ii) providing moderate thermal insulation in the combustion chamber, either by newlinedepositing thin ceramic material or by metal inserts (iii) employing high-octane fuel, such as methanol, ethanol, eucalyptus oil, and orange oil, as a blending agent with gasoline. newlineBased on the effectiveness of the above measures, an optimized design was developed in the final phase to achieve improved performance. Test results indicate that with an optimized two-stroke SI engine, the maximum percentage improvement in brake thermal efficiency is about 32%, together with a reduction of 3500 ppm in hydrocarbons (HC) and 2.9% by volume of carbon monoxide (CO) emissions over the normal engine (at