# Advances in Diesel-LNG Internal Combustion Engines
## 2 Results
### 2F Diesel-LNG ICEs R&D
Despite other significant differences, the relative change in emissions in response to the parametric changes was similar for a single hole and paired hole nozzles. The paired hole nozzle produced larger soot aggregates as well as larger numbers of particles. There were no significant changes in the soot primary particle size. Reference [50] supplies an overview of the improvements in the Westport HPDI 2.0, as well as performance and emissions results. The new generation HPDI delivers significant advantages vs. the baseline diesel in terms of performance and emissions. Further improvements vs. the first generation HPDI are also evidenced. The potential and challenges of adopting higher injection pressures are also highlighted. Reference [51] uses the Westport HPDI ICE to study both diffusion-controlled and partially premixed combustion strategies. The partially premixed combustion is called DI\({}_{2}\). The DI\({}_{2}\) combustion strategy is promising. It improves ICE efficiency by two efficiency points compared to the traditional diffusion combustion. The DI\({}_{2}\) is also studied in [52], where a partially premixed fuel-air charge is obtained by injecting the NG during the compression stroke. This injection is then followed by the diesel-injection-ignition. This combustion strategy improves the thermal and combustion efficiencies over the traditional fumigated 2F ICEs. This is by no way a surprise. DI\({}_{2}\) also supplies significant improvements in thermal efficiency over the baseline diffusion combustion strategy of HPDI. Injecting some NG prior to the diesel ignition injection thus sometimes provides better results than injecting the NG after diesel ignition injection. The opportunity depends on the specific speed and loads operating point. References [53; 54] study the effect of injection strategies on emissions from an HPDI ICE. The two works report the two parts of the same experience. Part I investigates the effect of late post-injection (LPI). Part II investigates slightly premixed combustion (SPC). The criteria for comparison are emissions and performance. In the SPC operation, the diesel injection is delayed, allowing more premixing of the NG before ignition. SPC operation at high load reduces 90% of the PM with a 2% improvement in fuel efficiency while delivering the almost same level of NOx. Drawbacks of SPC are cycle-to-cycle variation and excessive pressure rate of rising. PM does not increase for SPC with higher EGR level, higher global oxygen-based equivalence ratio (EQR) or higher pilot mass, which normally increases PM in mixing-controlled HPDI combustion. In the traditional diffusion combustion, there is too much fuel-rich stoichiometry at the time the NG is ignited. With SPC, the mass of fuel in the rich zone is less than 10% of the fuel in the rich zone of the mixing-controlled combustion. The potential for soot formation is thus drastically reduced. The morphology of particles produced by SPC is similar to the morphology of particles produced from the conventional diffusion combustion. The size and number concentration are however reduced. The post-injection of [53; 54] typically accounts for 10-25% of the total fuel mass. It occurs after the main combustion event. LPI produces significant PM reductions. There are only minor other effects on other pollutant emissions and performance. The morphology of particles produced by LPI is similar to the morphology of particles produced from the conventional diffusion combustion. The size and number concentration are however reduced. The main PM reduction of LPI originates from the smaller amount of fuel in the first injection, which is leading to a lower PM formation in the main combustion event. The second injection makes an insignificant contribution to the total PM. Significant advances have been recently achieved in CI hydrocarbon ICEs for racing car applications. Novel 2F diesel-LNG CI ICEs may certainly receive help from these experiences.