**5. Implications and justifications**

The increased utilization of HDRD as transport engine fuel has triggered renewed interest in R & D and funding of the production infrastructure across the globe. Also, the share of HDRD in global biofuel moved from about 5% in 2019 to about 10% in 2021 is pointed to its increased global production capacity. This trend, which is expected to continue, typifies the concerted efforts by countries to increase their share of renewable fuel in their energy mix. The simple production method, low cost feedstock, ecofriendly nature, improved performance, and moderate emission generated from HDRD, in comparison with PBD and biodiesel makes HDRD a fuel of the future.


**Table 6.**

*Comparison of PBD and biodiesel with HDRD.*

The outcome of most research showed that HDRD increased the BTE of the tested CI engine by more than 20%. For example, Kumar et al. [17] reported an increase in BTE from 21 to 23% at lower engine loads. However, at higher loads, a 34%, 36% and 32% increment were recorded at 40%, 80%, and 100% engine loads, respectively. In terms of emission, most studies reported a reduction of about 15%, 30%, 35%, and 75% reductions in NOx, HC, CO, and smoke emission at full load conditions. However, some authors reported that the NOx is unchanged while some reported an increased NOx emission from HDRD fueled CI engine. The aggregate of opinions suggests that HDRD performs better and generates fewer emissions than biodiesel, and PBD. This is very significant because it justifies increased investment in the production and utilization of HDRD.

When compared with HDRD with PBD and biodiesel, available information shows the preference for HDRD by most researchers and consumers. For example, using the major performance criteria, HDRD performed better as ICEs fuel than PDF and biodiesel. Also, the cost of production of HDRD is comparably lower than that of biodiesel. Just like biodiesel, HDRD is generated from lignocellulosic biomass, waste oils, and animal fats. HDRD is not only ecofriendly, and cost effective but also safeguards the environment by emitting fewer toxic gases. **Table 6** compares the performance, emission, production, and application of PBD, biodiesel, and HDRD.
