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Stringent emission regulations on one hand and increasing demand for better fuel economy along with lower noise levels on the other hand require adoption of advanced common-rail direct-injection technologies in diesel engines. In the present work, a small 0.9-l, naturally aspirated, two-cylinder, common-rail direct-injection diesel engine is used for the analysis of combustion noise at different engine operating conditions. Experiments are conducted at different loads and engine speeds, incorporating both single and multiple (i.e. pilot and main) injections along with different injection timings. In the case of multiple injections, the influence of pilot injection quantity is also evaluated on the combustion noise while maintaining the same load. In-cylinder pressure was recorded with the resolution of 0.1 crank angle degree, and it was used for the quantitative analysis of noise assessed from the resulting cylinder pressure spectra, and sound pressure level.

In a direct-injection (DI) engine, charge motion and mixture preparation are among the most important factors deciding the performance and emissions. This work was focused on studying the effect of injector positioning on fuel-air mixture preparation and fuel impingement on in-cylinder surfaces during the homogeneous mode of operation in a naturally aspirated, small bore, 0.2 l, light-duty, air-cooled, four-stroke, spark-ignition engine modified to operate under the DI mode. A commercially available, six-hole, solenoid-operated injector was used. Two injector locations were identified based on the availability of the space on the cylinder head. One location yielded the spray-guided (SG) configuration, with one of the spray plumes targeted towards the spark plug. In the second location, the spray plumes were targeted towards the piston top in a wall-guided (WG) configuration so as to minimize the impingement of fuel on the liner.

A direct-injection and spark-ignition single-cylinder engine with optical access to the cylinder was used for the combustion visualization study. Gasoline and ethanol-gasoline blended fuels were used in this investigation. Experiments were conducted to investigate the effects of fuel injection pressure, injection timing and the number of injections on the in-cylinder combustion process. Two types of direct fuel injectors were used; (i) high-pressure production injector with fuel pressures of 5 and 10 MPa, and (ii) low-pressure production-intent injector with fuel pressure of 3 MPa. Experiments were performed at 1500 rpm engine speed with partial load. In-cylinder pressure signals were recorded for the combustion analyses and synchronized with the high-speed combustion imaging recording. Visualization results show that the flame growth is faster with the increment of fuel injection pressure.

An experimental study has been conducted to quantify the velocity and pressure inside an idealized intake manifold of a motored internal combustion engine assembly. The aim of this work is to provide the real-time boundary conditions for more accurate multi-dimensional numerical simulations of complex in-cylinder flows in an internal combustion engine as well as the resultant in-cylinder flow patterns. The geometry of the intake manifold is simplified for this purpose. A hot-wire anemometer and a piezoresistive absolute pressure transducer are used to measure the velocity and pressure, respectively, over a plane inside the circular section of the intake manifold. In addition, pressure measurements are performed over an elliptical section near the intake port. Phase-averaged velocity and pressure profiles are then calculated from the instantaneous measurements. Experiments were performed at 900 and 1200 rpm engine speeds with wide open throttle.

In many Asian countries a significant automobile market share is held by two and three wheelers. Generally, cost and simplicity considerations limit the performance and emission levels of small engines. Methanol is an excellent alternative fuel for SI engines due to its high-octane number, high flame speed, presence of oxygen in its molecule and thus can be used to enhance the performance of small engines. However, use of neat methanol in SI engines poses constraints due to low energy density and poor vaporization characteristics. Also, the effectiveness of methanol as a fuel has still to be thoroughly investigated in small-bore SI engines in order to assess its potential. In this work, a small-bore 200cc three-wheeler automotive engine was modified to operate in the port fuel injection mode with neat methanol as the fuel.

Cycle-to-cycle flow variations significantly influence the combustion variations from one cycle to the next, particularly at low operating loads in small spark-ignition engines. Hence in the present work, cycle-to-cycle flow variations are analyzed at low throttle opening of 25% in a small spark-ignition engine using particle image velocimetry (PIV) technique. Experiments are conducted in an optically accessible single-cylinder, port-fuel-injection engine (volume: 110 cm3) at 1200 rpm engine speed. Images are captured at different crank angle positions during both intake and compression strokes over a tumble measurement plane bisecting the intake and exhaust valves, and processed using cross-correlation method to obtain the instantaneous velocity fields considering 200 image pairs at each crank angle position considered.

Nowadays, emission regulations and the requirement to reduce greenhouse gas emissions have escalated engine development efforts. In the present work, the effect of compression ratio on the performance, combustion and emission characteristics of a spark-ignition engine is evaluated at different operating conditions. A single-cylinder, water-cooled, spark-ignition engine (modified from a compression-ignition version) was used, with combustion chamber geometry consisted of flat cylinder head and a hemispherical bowl in the piston. Results showed that the brake thermal efficiency was increased from 9.8% to 12.9% when compression ratio was increased from 6.7:1 to 9.4:1 at low operating load of 5 N-m. Carbon monoxide emission was decreased when compression ratio was increased at all operating loads. However, as expected, nitric oxide emission was increased with the increase in compression ratio, with lower difference at low loads compared to medium and high loads.

A single-cylinder gasoline direct-injection engine was used for fuel spray and combustion visualizations with optical access to the combustion chamber. Experiments were conducted to investigate the effect of fuel injection pressure on spray and combustion characteristics inside the engine cylinder. A multi-hole high-pressure production injector was used with fuel pressures of 5 and 10 MPa. A Mie scattering technique was used to image the liquid phase of the fuel dispersion. The obtained spray images were then used to study the macroscopic spray characteristics such as spray structure, spray tip penetration and spray angle. Combustion visualization tests were performed to evaluate the effect of fuel injection pressure on combustion characteristics. In-cylinder pressure signals were recorded for the combustion analyses and synchronized with the high-speed combustion imaging recording.

The aim of this work is to study the combustion and gaseous emissions characteristics of a diesel engine dual-fueled with natural gas at different operating conditions (light to full load) for generator application. The electromechanical system was composed of a commercially available 18 liter, 6-cylinder diesel engine, coupled with the generator rated at 600 kWe at full-load. The flow of natural gas was electronically controlled using a throttle valve, and was inducted in the intake manifold before being introduced into the combustion chambers. Gaseous emissions of carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx) were measured under both diesel and dual fuel operations at different loads. This work also presents the effects of diesel oxidation catalyst to reduce HC and CO emissions under dual fuel operation. At each operating load, gas percentage was increased with corresponding decrease in diesel pilot while maintaining the same power output.

Nowadays, due to stringent emission regulations, it is imperative to incorporate modeling efforts with experiments. This paper presents the development of a phenomenological model to investigate the effects of various in-cylinder strategies on combustion and emission characteristics of a common-rail direct-injection (CRDI) diesel engine. Experiments were conducted on a single-cylinder, supercharged engine with displacement volume of 0.55 l at different operating conditions with various combinations of injection pressure, number of injections involving single injection and multiple injections with two injection pulses, and EGR. Data obtained from experiments was also used for model validation. The model incorporated detailed phenomenological aspects of spray growth, air entrainment, droplet evaporation, wall impingement, ignition delay, premixed and mixing-controlled combustion rates, and emissions of nitrogen oxides (NOx) and diesel soot.