The main challenge on the fueling of pure hydrogen in the automotive vehicles is the limitation in the hydrogen separation from the product of steam reforming and gasification plants and the storage issues. On the other hand, hydrogen fueling in automotive engines has resulted in uncontrolled combustion. These are some of the factors which motivated for the fueling of raw syngas instead of further chemical or physical processes. However, fueling of syngas alone in the combustion chamber has resulted in decreased power output and increased in brake specific fuel consumption. Methane augmented hydrogen rich syngas was investigated experimentally to observe the behavior of the combustion with the variation of the fuel-air mixture and engine speed of a direct-injection spark-ignition (DI SI) engine. The molar ratio of the high hydrogen syngas is 50% H₂ and 50% CO composition. The amount of methane used for augmentation was 20% (V/V). The compression ratio of 14:1 gas engine operating at full throttle position (the throttle is fully opened) with the start of the injection selected to simulate the partial DI (180° before top dead center (BTDC)). The relative air-fuel ratio (λ) was set at lean mixture condition and the engine speed ranging from 1500 to 2400 revolutions per minute (rpm) with an interval of 300 rpm. The result indicated that coefficient of variation of the indicate mean effective pressure (COV of IMEP) was observed to increase with an increase with λ in all speeds. The durations of the flame development and rapid burning stages of the combustion has increased with an increase in λ. Besides, all the combustion durations are shown to be more sensitive to λ at the lowest speed as compared to the two engine speeds.

Adjusted CO₂ (grams/mile) emissions fuel economy (miles/galons) from model year 1975-2016

The study was conducted in according to the SAE standards of Engine Power Test Code. The research test engine used in the current study is a DI SI, four-stroke engine with a compression ratio (r) of 14:1, cylinder bore of 76 mm, stroke length of 88 mm and number of valves 4. The schematics and the rating of the test bed are presented in Fig. 2 and Table 1, respectively. Fig. 3 shows the valve timing diagram of the engine to show the duration of openings of the inlet and exhaust valves. To measure the brake torque, to control the operation speed and to motor the engine at the time of no firing, the engine was attached to an eddy current dynamometer. Controlling of the air-fuel ratio (injection duration), ignition timing and injection timing was attained through the engine control unit (ECU). The details methodology followed in the current work is stated in another publication. The speed and engine torque was controlled by the dynamometer. The mixture ratio and the operation speed influences the combustion behavior of the engine. In order to have the clear mapping of the combustion behavior, the effect of air-fuel ratio and operation speed on the combustion was investigated for a methane augmented hydrogen rich syngas. Due to the limited pulse width of the injector, the current work is focused only on the lean operation condition where the minimum value of excess air ratio (λ) was limited to 1.25. The start of injection (SOI) = 180° CA before top dead center (BTDC) was found the optimum injection timing for the methane augmented hydrogen rich syngas in a separate study. SOI = 180° CA BTDC, which is before the inlet vale closing (132° CA before top dead center (BTDC)) is classified as a partial direct injection as injection starts before the closing of the inlet valve. Therefore, this injection timing was preferred in the study of the effect of air-fuel ratio at wide open throttle (the throttle is fully open) by varying only the fuel induction quantity. Fig. 2 shows the schematics of the setup used in the study.

Schematics of the DI SI engine

Combustion Efficiency: Engine speed and air-fuel ratio affect the combustion efficiency of the engine. Optimizing these parameters ensures more complete combustion of the fuel-air mixture, leading to increased engine efficiency and power output.

Knock Resistance: Controlling engine speed and air-fuel ratio can help minimize emissions of pollutants such as nitrogen oxides (NOx), carbon monoxide (CO), and unburned hydrocarbons (HC). Proper tuning can lead to cleaner combustion, reducing environmental impact.

Power Output: Engine speed and air-fuel ratio affect the knock resistance of the engine. Knock, or detonation, can occur when the air-fuel mixture ignites spontaneously due to high pressure and temperature in the combustion chamber. By adjusting these parameters, engineers can mitigate knock, improving engine durability and performance.

Fuel Economy: Engine speed directly correlates with power output. Higher engine speeds generally result in increased power output, which can be beneficial for certain applications requiring high performance. However, operating at excessively high speeds may lead to reduced efficiency and increased wear and tear on engine components.

IMEP (a), COV versus λ (b), COV verses λ and bmep comparison for CNG and MAHRS (c, d) for various engine speeds at 180oCA BTDC injection timing.

Environmental Regulations: With increasing environmental concerns and stringent emissions regulations globally, there is a growing demand for cleaner and more efficient engine technologies. Optimizing combustion in DI SI engines using alternative fuels like methane-augmented hydrogen-rich syngas can help meet these regulations by reducing emissions of greenhouse gases and pollutants.

Energy Security: As the world seeks to reduce dependency on fossil fuels and transition to renewable energy sources, there is a growing interest in alternative fuels such as hydrogen and syngas. These fuels can be produced from renewable resources, providing a more sustainable and secure energy supply.

Efficiency and Performance: Engine manufacturers are constantly striving to improve the efficiency and performance of their products. Optimizing engine speed and air-fuel ratio in DI SI engines can lead to better combustion efficiency, increased power output, and enhanced overall performance, thereby meeting the demands of various industries and applications.

Hydrogen Economy Development: The concept of a hydrogen economy, where hydrogen serves as a clean and sustainable energy carrier, is gaining momentum. Methane-augmented hydrogen-rich syngas can play a crucial role in this transition by providing a bridge between conventional fossil fuels and hydrogen-based technologies.

MFB curves versus CAD for different λ at 180oCA BTDC.