Search Results

The gaseous fuels, hydrogen and methane, are fuels that will likely be in adequate supply when crude oil sourced liquid fuels are scarce. These gases may he used directly in engines, which may need modification or could be used as feed stocks for liquid fuel synthesis. The energy efficiency of using methane and hydrogen in dedicated engines is compared with liquid fuelled engines. Hydrogen gives 6 3% improved efficiency and Methane 39% in city driving and Methane gives slightly improved power but Hydrogen fuel causes a 25% power loss compared with petrol. The storage of Methane in compressed or liquid form and Hydrogen in metal hydrides are compared. The overall efficiency of these gaseous fuel systems are compared, and fuel synthesis is included.

The hydrogen assisted jet ignition system (HAJI) replaces the spark plug of an Otto cycle engine and consists of a very small pre-chamber into which a hydrogen injector and spark plug are installed. The HAJI system allows stable combustion of very lean main-chamber hydrocarbon mixtures, leading to improved thermal efficiency and very much reduced NOx emissions. The current investigation focuses on the application of HAJI to a modern pent-roof, four valve per cylinder automotive engine. The development of a new hydrogen injection system and HAJI pre-chamber based on proprietary gasoline and diesel injectors is described. Results from injector and engine performance testing are presented in detail.

The HAJI (Hydrogen Assisted Jet Ignition) system for S.I. engines utilises direct injection of small amounts of hydrogen to enhance the combustion of a variety of automotive fuels. Although not the primary purpose of HAJI, the hardware, once in place, also lends itself to the possibility of hydrogen-only running during a cold start. Cold-start simulations have been performed using a single cylinder engine. Results are presented, comparing hydrogen-only tests with standard HAJI operation and normal spark-ignition operation. HAJI and spark ignition tests were carried out with gasoline as the main-chamber fuel. Emission levels and combustion stability characteristics were recorded as the engine warmed up. The differences between the various fueling/ignition scenarios are presented and the implications for possible automotive applications are discussed in light of current and proposed emissions legislation.

The goal of hydrogen engine research is to achieve highest possible efficiency with low NOx emissions. This is necessary for the hydrogen car to remain competitive with the ever-improving efficiency of conventional fuel's use, to take advantage of the increased availability of hydrogen distribution for fuel cells and to achieve better range than battery electric vehicles. This paper examines the special problems of hydrogen engine combustion and ways to improve efficiency. Central to this are the effects of compression ratio (CR) and lambda (excess air ratio) and ignition system. The results demonstrate highest indicated thermal efficiency at ultra lean condition of lambda ≻ 2 and with central ignition. This need for this lean mixture is partly explained by the higher heat transfer losses.

HAJI (Hydrogen Assisted Jet Ignition) is an advanced combustion initiation system for otherwise standard S.I engines. It utilises the fluid mechanics of a turbulent, chemically active jet, combined with the reliability of spark igniting rich hydrogen mixtures. The result is an extremely robust ignition system, capable of developing power from an engine charged with air-fuel mixtures as lean as λ = 5. Experiments have been performed using a single cylinder engine operating on gasoline in the speed range of 600-1800 r/min. Data are presented in the form of maps which describe fuel efficiency, combustion stability and emissions with respect to load, speed, air-fuel ratio and throttle. The results are incorporated into a model of a known engine and vehicle and this is used to estimate performance over the Federal drive-cycle.

This paper presents a study of the performance of a 6-cylinder, spark-ignited, port-fuel-injected, production engine modified for hydrogen fueling. The engine modifications include turbo-charging, multiple fuel injectors per port and charge-dilution control techniques. Pumping losses are reduced through ultra-lean burn and throttle-less operation alongside high charge dilution ratio control achieved by twin independent variable cam timing without external EGR. Lean-burn combustion, engine-out emissions and brake thermal efficiency results are examined in detail. In particular, low NO emissions and brake thermal efficiencies near 38% are observed experimentally at the same operating conditions. The former is explained in terms of the usual thermal NOx pathway. Usage of throttle position, injection timings and cam timings for avoiding preignition and knock over the entire engine map are also discussed.

HAJI, or Hydrogen Assisted Jet Ignition, is an ignition system which uses a hot gaseous jet to initiate and stabilise combustion. HAJI allows a dramatic reduction of cyclic variability, and an extension of the lean limit of the engine to lambda 5. Improvements in cyclic variability lead to increased power output, reduced noise, wear on components and emissions. The ability to operate ultra lean gives 25% improvements in efficiency and extremely low emissions, particularly of NOx. Combustion analysis based on the fractal dimensions of the propagating flame fronts, obtained from optical flame data, support the hypothesis of enhancement of flame speeds through the presence of active chemical species. However, the relative contributions of turbulence and active species to the mechanisms of combustion enhancement realised with HAJI are not well defined. HAJI ignition has also been simulated with a comprehensive three dimensional combustion code, KIVA3.