In countries with limited financial resources and access to new technologies, as well as difficult environmental conditions, the process of renewing urban transport infrastructure is a complex process. An example is Africa, especially Ethiopia. Ethiopia is assessing compressed natural gas as a transport fuel for intercity buses currently powered by ageing diesel engines. This study reports a controlled before and after comparison of a single 12 m coach tested in its original Euro III diesel configuration and after replacement with a 6.7 L spark-ignited CNG engine equipped with stoichiometric control, exhaust gas recirculation, and a three-way catalyst. Chassis dynamometer tests were performed using the world harmonized transient cycle (WHTC) and a locally defined intercity cycle, followed by repeated on road measurements on the Addis Ababa-Adama corridor using a portable emissions measurement system. Distance-based emission factors for carbon monoxide (CO), total hydrocarbons (THC), nitrogen oxides (NOx), particulate matter (PM), and carbon dioxide (CO2) were determined from diluted exhaust measurements. Under both cycles, the CNG configuration yielded lower NOx, particulate, and CO2 emissions than diesel. Hydrocarbon emissions increased under both cycles, while CO increased under the WHTC and on the road but decreased slightly under the intercity cycle. On-road measurements confirmed the same directional trends. Fuel consumption and operating cost were evaluated from measured fuel use and local retail prices. A fleet scenario was derived from the measured emission factors and stated activity assumptions. The results indicate that engine-replacement CNG conversions reduced NOx and particulate emissions in Ethiopian intercity service.
The variability of primary emission signals from high-pressure turbine blades originating from the same stage of an SO-3 turbojet engine was evaluated using Laser Ablation coupled with Microwave-Induced Plasma Optical Emission Spectrometry (LA-MIP OES). Forty turbine blades were investigated, with one analytical measurement performed for each blade. Direct solid sampling enabled multi-element analysis without chemical sample preparation. The primary emission signal intensities of nickel, molybdenum, chromium, cobalt, and aluminum were statistically evaluated using mean values, standard deviations, coefficients of variation, interquartile ranges, confidence intervals, and boxplot analysis. The coefficients of variation ranged from 3.44% to 11.60%, indicating relatively low variability of the measured emission signals among the investigated blades. The lowest variability was observed for cobalt, nickel, and molybdenum, whereas chromium exhibited the highest dispersion. The results demonstrate a high degree of uniformity of the measured emission signals and indicate the potential of LA-MIP OES for comparative assessment of turbine blade materials.
Injection timing effects on combustion intensity redistribution and pressure-induced mechanical loading were evaluated for a turbocharged diesel engine using a calibrated Diesel-RK simulation model. Engine simulations were performed at multiple load conditions with systematic variation of injection timing. Advancing injection timing shifted combustion toward top dead center, accelerating pressure development and increasing the maximum pressure rise rate from approximately 1.2–1.6 bar/°CA to values exceeding 5 bar/°CA under advanced conditions. The maximum piston gas force increased from 55–70 kN to over 100 kN at high load. The results demonstrated that mechanical loading depended on both pressure magnitude and pressure-development rate, indicating a coupled combustion–pressure interaction rather than a single-parameter response. The results showed that mechanical loading depended on both pressure magnitude and pressure-rise behaviour rather than on a single pressure parameter. Increasing pressure-rise rate intensified piston gas-force response, particularly under advanced injection and high-load operation. The results also indicated that combustion-optimal injection timing did not necessarily correspond to mechanically favourable operating conditions.
The article presents the results of engine tests aimed at assessing the impact of modifications to engine control software on emission parameters and fuel consumption. Experiments were conducted on a 1.3 L MultiJet compression-ignition engine compliant with the Euro 6 standard. The electronic control unit's EEPROM was extracted and re-calibrated by a leading chiptuning company. Two operating scenarios-factory calibration and the modified calibration-were executed on an engine test bench equipped with a dynamic dynamometer. To ensure repeatability and comparability, the dynamometer governed engine speed and load in accordance with the New European Driving Cycle (NEDC) homologation procedure. Analysis of the revised calibration maps revealed substantive alterations, chiefly to the boost-pressure characteristic, the maximum-torque map, and the maximum fuel-injection-quantity map as a function of air mass. The resulting emission data demonstrate that chip-tuning exerts a pronounced impact on the engine's emission profile, elevating the release of toxic exhaust constituents, most notably nitrogen oxides.
This paper presents an analysis of the impact of the marine environment on selected components of a ship hybrid propulsion system, including the PEMFC/BOP section (auxiliary equipment), structural elements and mountings. The analysis was carried out for Baltic Sea conditions, with four seasons, two exposure levels and North Sea reference scenarios with high chloride deposition. Four mutually complementary assessment areas were considered: thermal-moisture, corrosion, electrochemical and dynamic effects. The thermal-moisture part was described using a heat balance and the dew point. Corrosion effects were determined from chloride deposition S_d and the ISO 9223 dose-response function. The PEM electrochemical part was represented using the Springer relations and the Tafel equation, whereas the dynamic part was described using the JONSWAP spectrum, the RAO operator and the rms acceleration a_rms. The scenarios were compared using the proposed decision metric R*. The results indicate that the total environmental load results from the simultaneous influence of condensation, corrosion, electrochemical loading and dynamics, with individual mechanisms dominating under different operating conditions. In particular, two main sources of risk were separated: a humid-salt environment, which intensifies corrosion processes, and dry conditions, which reduce membrane hydration and increase the electrochemical load of the FC section. The study also shows that suitably selected protective measures and changes in system configuration can significantly reduce the overall environmental impact in terms of corrosion as well as dynamic and electrochemical loads. The proposed approach may be used as a preliminary environmental qualification tool and as a basis for planning further validation tests.
