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Direct Injection (DI) is believed to be one of the key strategies for maximizing the thermal efficiency of Spark Ignition (SI) engines and meet the ever-tightening emissions regulations. This paper explores the use of Liquefied Petroleum Gas (LPG) liquid phase fuel in a 1.5 liter SI four cylinder gasoline engine with double over head camshafts, four valves per cylinder, and centrally located DI injector. The DI injector is a high pressure, fast actuating injector enabling precise multiple injections of the finely atomized fuel sprays. With DI technology, the injection timing can be set to avoid fuel bypassing the engine during valve overlap into the exhaust system prior to combustion. The fuel vaporization associated with DI reduces combustion chamber and charge temperatures, thereby reducing the tendency for knocking. Fuel atomization quality supports an efficient combustion process.

Direct Injection (DI) is believed to be one of the key strategies for maximizing the thermal efficiency of Spark Ignition (SI) engines and meeting the ever-tightening emissions regulations. This paper explores the use of propane and methane gas fuels in a 1.5 liter SI four cylinder gasoline engine with double over head camshafts, four valves per cylinder, and a centrally located DI injector. With DI technology, the injection timing can be set to avoid fuel bypassing the engine during valve overlap into the exhaust system prior to combustion. DI of fuel reduces the embedded air displacement effects of gaseous fuels and lowers the charge temperature. Injection timings and compression ratio are optimized for best performances at Wide Open Throttle (WOT) conditions when configured to achieve homogeneous charge at stoichiometry or run lean jet controlled stratified.

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.

Oxygen-enriched air supplied to a diesel engine has significant benefits in reducing the particulate emissions of all fuels tested. A Caterpillar 3208 direct injection diesel engine was modified to operate on a wide range of fuel grades including residual fuel oils with oxygen-enriched intake air. The paper focuses on four fuels, two fuels were regular automotive distillate fuels, the third was a low emission diesel fuel and the fourth fuel had high boiling point fractions. Comparison with less extensive work on residual fuel oil is also included. Smoke and particulates decrease by up to 94% at full load with 27% oxygen concentration. Performance with oxygen addition using regular fuels showed comparable smoke and particulates to a premium priced low emission fuel used specifically in underground mines.

Diesel engines are used in heavy duty applications because of their high efficiency and reliability. However, their high diesel particulates and NOx emissions remain major concerns. An eight cylinder direct injection diesel engine was connected to a partial flow particulate sampling mini-dilution tunnel. Six different grades of diesel fuels were studied for their regular emissions as well as smoke and particulate emissions. Each fuel was tested at three engine speeds and full load. This paper presents the results of these tests which includes analysis of the effects of load, cetane number, 90% distillation temperature, and density for steady state conditions. A correlation was developed for converting smoke numbers in Hartridge Smoke Units (HSU) to the specific particulate emissions by evaluating results of all fuels tests. Another correlation was also developed for diesel particulates and NOx emissions trade-off.

The gross emissions for the Australian vehicle fleet are forecast from estimates of population growth, vehicle ownership and vehicle in-service performance. These estimates are coupled with sensitivity analyses, to emissions deterioration and on-road performance and the impact of alternative fuels. It is concluded that more data on precontrol and high mileage controlled vehicles is needed to remove uncertainties in the projections. The results indicate that existing vehicle emission control standards will continue to give beneficial reductions in hydrocarbon emission levels through to 1995 and present levels will not be exceeded this century. Ambient ozone trends have fallen and are qualatatively in accord with reducing vehicle emissions.

This paper presents procedures for calculating the emissions of the population-average diesel- and gasoline-fueled vehicles in a range of operating modes. These procedures, together with a simple, but flexible, model of vehicle driving patterns, are used to show how changes in traffic flow and driving patterns can influence the vehicular source of emissions along urban roadways. The procedures are applied to predict emission rates in hypothetical traffic flows and in real traffic conditions as measured in central Edinburgh, Scotland, where the relative contributions of individual traffic groups to the vehicular emission sources have been assessed.

The exhaust emissions from a single-cylinder spark ignition engine were measured as a function of burning time. Flame propagation time was measured with an ionization probe, and the exhaust gas was sampled with a gas sampling valve. Electronic control logic determined the cycles to be sampled, based on the flame propagation time. Tests were carried out at full throttle, for lean, optimum, and rich A/F. The exhaust components measured were CO, HC, O2, H2, and N2 using a gas chromatograph. The emission most affected by CBCV is CO. Cycles that are either faster or slower than the mean cycle have increased CO, particularly at lean A/F where a five-fold difference in CO concentration was measured. HC emissions show a 150% change for the same conditions. For other than lean A/F operation, H2 was an exhaust product, up to 6% at rich A/F operation. It is well established that reductions in CBCV would improve efficiency and power output.

The paper describes procedures for predicting the course of reaction and the onset of autoignition in homogeneous fuel-air mixtures, using detailed chemical kinetic data and considering hydrogen gas as a fuel. Experimental results from both a motored autoigniting engine and a pneumatically driven compression apparatus are then compared with computational predictions. It is shown that, depending on the reliability and completeness of the kinetic scheme employed, reasonably good agreement between computed and observed pressure development records can be obtained.

The arguments are given for the application of a 1.3 litre turbocharged spark ignition engine, as a substitute for a 2 litre normally aspirated engine as the power plant for a compact-sized car in the late 80’s. Three stages of the project leading to an optimised engine-turbocharger package are outlined. Achievement of Stage 1, leading to evaluation of a non-optimised configuration, will be reported. Description includes the use of a separately driven supercharger to define operating limits in the experimental variable matrix comprising compression ratio, boost pressure, EGR rate and spark retard at the knock limit. Computer programs for the optimising stages of the project are outlined. The current status of the project is reported, where, even at this early stage, fuel consumption reductions of 11-22% have been achieved under simulated urban driving conditions.

The mathematical equations describing the momentum, energy and mass exchanges in non-firing engine cylinders are described and solved. Attention is confined to laminar flow in axi-symmetric cylinders. Pressure development and velocity prediction, for plane cylindrical combustion chambers, compare favourably with experimental measurements for compression] and expansion in motored engines. At engine speeds less than 100 rev/min the piston motion induces a toroidal vortex during compression whose direction is not reversed on expansion. Conductive heat transfer at higher engine speeds, 600-1000 rev/min, adequately describes the gas-wall heat-transfer. Flow patterns are also predicted for a diesel-type bowl in piston configuration.

The effect of combustion time and combustion variability on performance and emissions was investigated with a single cylinder CFR spark ignition engine using gaseous fuel (propane). A system was developed which allowed the collection of the products of combustion of individual engine cycles. This system consisted of an alectrically operated gas sampling valve drawing gas from immediately behind the exhaust valve, and an electronic discriminator/valve driver system. Engine cycles were selected for sampling according to the time for flame propagation to a point in the combustion chamber diametrically opposite the spark site, this being a strong indicator of total combustion time. Flame arrival was detected with an ionisation probe. A Gas Chromatograph and a modified Chemiluminiscent NOX analyser were used for gas analysis. For any particular engine operating point, flame propagation time varies randomly from cycle to cycle (cycle by cycle variability).

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.

This paper presents experimental and computational results obtained on an in line, six cylinder, naturally aspirated, gasoline engine. Steady state measurements were first collected for a wide range of cam and spark timings versus throttle position and engine speed at part and full load. Simulations were performed by using an engine thermo-fluid model. The model was validated with measured steady state air and fuel flow rates and indicated and brake mean effective pressures. The model provides satisfactory accuracy and demonstrates the ability of the approach to produce fairly accurate steady state maps of BMEP and BSFC. However, results show that three major areas still need development especially at low loads, namely combustion, heat transfer and friction modeling, impacting respectively on IMEP and FMEP computations. Satisfactory measurement of small IMEP and derivation of FMEP at low loads is also a major issue.